feat: support SET TO DEFAULT

[yuhao-su]

sI hereby agree to the terms of the RisingWave Labs, Inc. Contributor License Agreement.

What's changed and what's your intention?

support SET TO DEFAULT for session config

#8851

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• I have added test labels as necessary. See details.
• I have added fuzzing tests or opened an issue to track them. (Optional, recommended for new SQL features Sqlsmith: Sql feature generation #7934).
• My PR contains breaking changes. (If it deprecates some features, please create a tracking issue to remove them in the future).
• All checks passed in ./risedev check (or alias, ./risedev c)
• My PR changes performance-critical code. (Please run macro/micro-benchmarks and show the results.)

• My PR contains critical fixes that are necessary to be merged into the latest release. (Please check out the details)

Documentation

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

We can set a session config parameter to default value by SET parameter_name TO DEFAULT

Release note

If this PR includes changes that directly affect users or other significant modifications relevant to the community, kindly draft a release note to provide a concise summary of these changes. Please prioritize highlighting the impact these changes will have on users.

[BugenZhao]

Please also specify the release notes and tag the PR user-facing.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (b196953) 68.31% compared to head (997812c) 68.32%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
src/frontend/src/session.rs	55.55%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13693   +/-   ##
=======================================
  Coverage   68.31%   68.32%           
=======================================
  Files        1523     1523           
  Lines      261833   261804   -29     
=======================================
+ Hits       178878   178884    +6     
+ Misses      82955    82920   -35     

Flag	Coverage Δ
rust	68.32% <85.71%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.