[cli] Fix output format of string by pulsar-admin command

[massakam]

Motivation

In Pulsar version 2.4.2 and earlier, the pulsar-admin command output a list of strings in the following format:

$ ./bin/pulsar-admin tenants list

public
pulsar
sample

On the other hand, in 2.5.0 and later versions, each string is enclosed in double quotes:

$ ./bin/pulsar-admin tenants list

"public"
"pulsar"
"sample"

This is due to #5313. With this change, strings are now displayed after being encoded to JSON. I think these double quotes are superfluous.

Modifications

If the type of the variable to be output is String, it will be output without JSON encoding.

Verifying this change

• Make sure that the change passes the CI checks.

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

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (no)
• The public API: (no)
• The schema: (no)
• The default values of configurations: (no)
• The wire protocol: (no)
• The rest endpoints: (no)
• The admin cli options: (no)
• Anything that affects deployment: (no)

[Anonymitaet]

Hi @tuteng Could you please help review this PR from the technical perspective? Thanks

[nkurihar]

@rdhabalia @sijie @merlimat
Any thoughts for this PR?

It looks good to 2.4.2 or earlier users (including me).
However it might be "breaking" for 2.5.0 or later users.

IMO the impact of this change is within only displayed messages and not large, so I approved.