RFR: 8332124: Jcmd processing should accept the "help" sub option as command argument

[Sonia Zaldana Calles]

Hi all, 

This PR addresses [8332124](https://bugs.openjdk.org/browse/JDK-8332124) enabling jcmd to accept "help" as an argument to subcommands. 

Testing: 
- [x] Verified running `jcmd 4711 VM.metaspace help` works along with other subcommands. 
- [x] Added test case passes. 

Thanks, 
Sonia

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Commit messages:
 - 8332124: Jcmd processing should accept the "help" sub option as command argument

Changes: https://git.openjdk.org/jdk/pull/19776/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19776&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332124
  Stats: 94 lines in 3 files changed: 94 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/19776.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19776/head:pull/19776

PR: https://git.openjdk.org/jdk/pull/19776