feat(frontend): support tab-completion for [ALTER SYSTEM] SET

[BugenZhao]

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What's changed and what's your intention?

Based on #15113 and #15108. Resolve #8850.

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Note that the session variables is always a subset of system parameters in Postgres' configuration system (Grand Unified Configuration, GUC), which does not hold in RisingWave.

As a result, psql will also auto-complete session variables for ALTER SYSTEM SET that are false positives. There's no elegant way to fix that as the query for auto-completion is automatically sent by the client. However, this is not a significant issue so we may simply leave it as it is.

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Documentation

• My PR needs documentation updates. (Please use the Release note section below to summarize the impact on users)

Release note

Support tab-completion for SET and ALTER SYSTEM SET commands in psql client.

[BugenZhao]

Current dependencies on/for this PR:

• main
  • PR feat(frontend): add description column for SHOW PARAMETERS #15113
    • PR feat(frontend): support tab-completion for [ALTER SYSTEM] SET #15123 👈
      • PR fix(frontend): require primary key for system table #15126

This stack of pull requests is managed by Graphite.