RFR: 2124: SKARA Commands Intercepted By GitLab

[Zhao Song]

The SKARA bot supports some pull request and commit commands.

However, some of these commands conflict with built-in commands in GitLab. To prevent the commands from be intercepted by GitLab, users need to add spaces before the command.Although we clearly documented this on our wiki page, users occasionally forget about it.

I remember someone suggested that we could introduce an optional 'skara' prefix to the command. For instance, '/skara label add test' would be equal to '/label add test'. I believe implementing this enhancement would make SKARA bot more user-friendly.

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Commit messages:
 - SKARA-2124

Changes: https://git.openjdk.org/skara/pull/1594/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1594&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2124
  Stats: 19 lines in 7 files changed: 8 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/skara/pull/1594.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1594/head:pull/1594

PR: https://git.openjdk.org/skara/pull/1594