[improve][cli] handle help flag properly

[tisonkun]

Motivation

Currently

$ ./bin/pulsar-admin schemas -h


Expected a command, got -h

Invalid command, please use `pulsar-admin --help` to check out how to use
2022-12-09T16:18:27,751+0800 [main] WARN  org.apache.pulsar.common.util.ShutdownUtil - Triggering immediate shutdown of current process with status 1
java.lang.Exception: Stacktrace for immediate shutdown
	at org.apache.pulsar.common.util.ShutdownUtil.triggerImmediateForcefulShutdown(ShutdownUtil.java:52) ~[pulsar-common.jar:2.11.0-SNAPSHOT]
	at org.apache.pulsar.admin.cli.PulsarAdminTool.exit(PulsarAdminTool.java:309) ~[pulsar-client-tools.jar:2.11.0-SNAPSHOT]
	at org.apache.pulsar.admin.cli.PulsarAdminTool.main(PulsarAdminTool.java:300) ~[pulsar-client-tools.jar:2.11.0-SNAPSHOT]

$ ./bin/pulsar-admin schemas delete -h


null

Reason: java.util.concurrent.CompletionException: org.apache.pulsar.client.admin.internal.http.AsyncHttpConnector$RetryException: Could not complete the operation. Number of retries has been exhausted. Failed reason: Connection refused: localhost/127.0.0.1:8080
2022-12-09T16:18:32,984+0800 [main] WARN  org.apache.pulsar.common.util.ShutdownUtil - Triggering immediate shutdown of current process with status 1
java.lang.Exception: Stacktrace for immediate shutdown
	at org.apache.pulsar.common.util.ShutdownUtil.triggerImmediateForcefulShutdown(ShutdownUtil.java:52) ~[pulsar-common.jar:2.11.0-SNAPSHOT]
	at org.apache.pulsar.admin.cli.PulsarAdminTool.exit(PulsarAdminTool.java:309) ~[pulsar-client-tools.jar:2.11.0-SNAPSHOT]
	at org.apache.pulsar.admin.cli.PulsarAdminTool.main(PulsarAdminTool.java:300) ~[pulsar-client-tools.jar:2.11.0-SNAPSHOT]

With this patch

$ ./bin/pulsar-admin schemas -h       


Usage: pulsar-admin schemas [options] [command] [command options]
  Commands:
    get      Get the schema for a topic
      Usage: get [options] persistent://tenant/namespace/topic
        Options:
          -a, --all-version
            all version
            Default: false
          -v, --version
            version

    delete      Delete the latest schema for a topic
      Usage: delete [options] persistent://tenant/namespace/topic
        Options:
          -f, --force
            whether to delete schema completely. If true, delete all resources 
            (including metastore and ledger), otherwise only do a mark 
            deletion and not remove any resources indeed
            Default: false

    upload      Update the schema for a topic
      Usage: upload [options] persistent://tenant/namespace/topic
        Options:
        * -f, --filename
            filename

    extract      Provide the schema via a topic
      Usage: extract [options] persistent://tenant/namespace/topic
        Options:
          -a, --always-allow-null
            set schema whether always allow null or not
            Default: true
        * -c, --classname
            class name of pojo
          -n, --dry-run
            dost not apply to schema registry, just prints the post schema 
            payload 
            Default: false
        * -j, --jar
            jar filepath
        * -t, --type
            type avro or json

$ ./bin/pulsar-admin schemas delete -h


Usage: pulsar-admin schemas delete [options] 
      persistent://tenant/namespace/topic 
  Options:
    -f, --force
      whether to delete schema completely. If true, delete all resources 
      (including metastore and ledger), otherwise only do a mark deletion and 
      not remove any resources indeed
      Default: false

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[codecov-commenter]

Codecov Report

Merging #18832 (0ee1a52) into master (da87e40) will increase coverage by 1.25%.
The diff coverage is 42.85%.

@@             Coverage Diff              @@
##             master   #18832      +/-   ##
============================================
+ Coverage     46.42%   47.68%   +1.25%     
- Complexity    10437    10625     +188     
============================================
  Files           703      703              
  Lines         68816    68838      +22     
  Branches       7377     7379       +2     
============================================
+ Hits          31950    32822     +872     
+ Misses        33252    32336     -916     
- Partials       3614     3680      +66     

Flag	Coverage Δ
unittests	47.68% <42.85%> (+1.25%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ache/pulsar/broker/loadbalance/LinuxInfoUtils.java	26.74% <0.00%> (-1.17%)	⬇️
...ker/resourcegroup/ResourceQuotaCalculatorImpl.java	4.16% <0.00%> (ø)
...ker/loadbalance/impl/LinuxBrokerHostUsageImpl.java	79.68% <100.00%> (+0.32%)	⬆️
.../service/SystemTopicBasedTopicPoliciesService.java	72.56% <100.00%> (+8.14%)	⬆️
...ker/loadbalance/impl/LeastLongTermMessageRate.java	73.33% <0.00%> (-20.00%)	⬇️
...ersistentStickyKeyDispatcherMultipleConsumers.java	46.07% <0.00%> (-14.71%)	⬇️
...ervice/persistent/MessageRedeliveryController.java	56.09% <0.00%> (-9.76%)	⬇️
...ker/resourcegroup/ResourceGroupConfigListener.java	57.53% <0.00%> (-6.85%)	⬇️
...g/apache/pulsar/client/impl/ConnectionHandler.java	50.00% <0.00%> (-5.32%)	⬇️
...g/apache/pulsar/broker/lookup/TopicLookupBase.java	50.27% <0.00%> (-3.92%)	⬇️
... and 81 more

[yuruguo]

LGTM