[fix][cli] Correct admin command documentation generation

[lhotari]

Motivation

pulsar-admin documents generate brokers prints the entire growing document after each subcommand. This produces 13 progressively longer copies of the brokers documentation and repeated entries in the reference site's sidebar. Generating multiple modules also repeats earlier modules.

The generator reads options from the command group instead of each subcommand, so generated reference pages omit actual command flags such as --primary, --secondary, and --unload-scope.

Modifications

• Print the completed document once through the command's configured output writer.
• Generate option tables from each subcommand's visible options, include initialized defaults, and keep table column counts consistent, including the functions language-support column.
• Deduplicate command aliases by canonical name and reset that tracking between invocations.
• Add five regression tests covering single and multiple modules, aliases, all-module generation, repeated invocations, and option table contents.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and was verified locally with:

./gradlew :pulsar-client-tools:test --tests org.apache.pulsar.admin.cli.TestCmdGenerateDocument -PtestRetryCount=0 -PtestFailFast=false quickCheck
./gradlew spotlessCheck checkstyleMain checkstyleTest

All five tests and the checks passed. The regression tests reproduced duplicate headings before the fix. Also generated all 21 admin command groups using the updated CLI: each document has one top-level heading, retains its subcommands, and has consistent option table columns. Checked the rendered brokers reference page in a local site preview.

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

• 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
• The metrics
• Anything that affects deployment