feat: add WAIT command

[kwannoel]

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

What's changed and what's your intention?

Closes #12885

Checklist

• I have written necessary rustdoc comments
• I have added necessary unit tests and integration tests
• 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)

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.

[kwannoel]

The wait logic.

[codecov]

Codecov Report

Merging #13027 (36e9bfe) into main (272eff4) will decrease coverage by 0.10%.
Report is 1 commits behind head on main.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main   #13027      +/-   ##
==========================================
- Coverage   68.69%   68.60%   -0.10%     
==========================================
  Files        1495     1496       +1     
  Lines      251161   251257      +96     
==========================================
- Hits       172546   172383     -163     
- Misses      78615    78874     +259     

Flag	Coverage Δ
rust	68.60% <0.00%> (-0.10%)	⬇️

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

Files	Coverage Δ
src/sqlparser/src/keywords.rs	100.00% <ø> (ø)
src/frontend/src/handler/mod.rs	58.40% <0.00%> (-0.18%)	⬇️
src/sqlparser/src/ast/mod.rs	85.40% <0.00%> (-0.07%)	⬇️
src/sqlparser/src/parser.rs	87.51% <0.00%> (-0.03%)	⬇️
src/utils/pgwire/src/pg_response.rs	52.80% <0.00%> (-0.30%)	⬇️
src/frontend/src/meta_client.rs	0.00% <0.00%> (ø)
src/frontend/src/test_utils.rs	72.19% <0.00%> (-0.31%)	⬇️
src/meta/service/src/ddl_service.rs	0.00% <0.00%> (ø)
src/rpc_client/src/meta_client.rs	4.03% <0.00%> (-0.02%)	⬇️
src/frontend/src/handler/wait.rs	0.00% <0.00%> (ø)
... and 1 more

... and 18 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[chenzl25]

Generally LGTM. Should we support canceling wait statement or set a maximum wait time to avoid a potential dead loop?

[BugenZhao]

Will this command be user-facing?

[BugenZhao]

avoid a potential dead loop

It's not a big deal. The loop will be cancelled once the gRPC connection closes, that is, the frontend cancels the request.

[kwannoel]

Will this command be user-facing?

Nope. Just for tests.