[improve][ci] Improve code coverage reporting

[lhotari]

Motivation

After reviewing the latest changes made in #19264 for collecting code coverage in a new way, there are a few details that need to be adjusted.
The Codecov results can be seen for the PR commit at
https://app.codecov.io/github/apache/pulsar/commit/62060c814bf90de9b8f7cd520e2dc5459b394cbe/tree
The build workflow run contained Jacoco html reports at https://github.com/apache/pulsar/actions/runs/3961486478 .

Modifications

• use test scope classpath to collect correct dependencies
  • exclude test projects so that coverage doesn't get reported for them
• show link to Codecov commit level report
• notify as soon as 4 uploads are completed for the commit
  • ignore the CI status since that is often wrong in Codecov and the notification doesn't appear at all.
  • It's sufficient to wait for 4 uploads to happen now that it happens consistently after [fix][ci] Fix Jacoco code coverage to report classes in dependent projects #19264 changes
• exclude shaded classes from Jacoco instrumentation to lower Jacoco's overhead
• excluded protobuf generated classes from Jacoco instrumentation

Documentation

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

[codecov-commenter]

Codecov Report

Merging #19296 (602f60f) into master (29c244a) will increase coverage by 10.04%.
The diff coverage is 87.93%.

@@              Coverage Diff              @@
##             master   #19296       +/-   ##
=============================================
+ Coverage     52.84%   62.89%   +10.04%     
- Complexity    22367    26118     +3751     
=============================================
  Files          1824     1895       +71     
  Lines        136749   137475      +726     
  Branches      15047    15091       +44     
=============================================
+ Hits          72264    86460    +14196     
+ Misses        56968    43085    -13883     
- Partials       7517     7930      +413     

Flag	Coverage Δ
inttests	23.99% <56.89%> (+1.63%)	⬆️
systests	25.59% <53.44%> (+0.58%)	⬆️
unittests	60.72% <86.20%> (+13.69%)	⬆️

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

Impacted Files	Coverage Δ
.../org/apache/pulsar/websocket/WebSocketService.java	72.02% <ø> (+5.82%)	⬆️
...che/pulsar/websocket/AbstractWebSocketHandler.java	42.02% <37.50%> (+1.31%)	⬆️
...pulsar/metadata/impl/MetadataStoreFactoryImpl.java	80.00% <92.85%> (+30.00%)	⬆️
...che/bookkeeper/mledger/impl/ManagedLedgerImpl.java	78.83% <100.00%> (+4.82%)	⬆️
...org/apache/pulsar/broker/ServiceConfiguration.java	98.70% <100.00%> (+0.43%)	⬆️
...apache/pulsar/metadata/impl/EtcdMetadataStore.java	81.43% <100.00%> (-1.48%)	⬇️
...pulsar/metadata/impl/LocalMemoryMetadataStore.java	87.85% <100.00%> (+0.35%)	⬆️
...che/pulsar/metadata/impl/RocksdbMetadataStore.java	72.94% <100.00%> (+0.28%)	⬆️
...g/apache/pulsar/metadata/impl/ZKMetadataStore.java	77.09% <100.00%> (+7.58%)	⬆️
...ta/impl/batching/AbstractBatchedMetadataStore.java	84.21% <100.00%> (ø)
... and 718 more