feat: implement the CreateFlowProcedure

[WenyXu]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

#3664

What's changed and what's your intention?

1. Add FlowMetadataManager and FlowMetadataAllocator to DdlContext.
2. Implement the CreateFlowProcedure

Tests will be added via another PR.

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

[codecov]

Codecov Report

Attention: Patch coverage is 39.82869% with 281 lines in your changes are missing coverage. Please review.

Project coverage is 85.33%. Comparing base (7ef18c0) to head (2590213).
Report is 2 commits behind head on main.

❗ Current head 2590213 differs from pull request most recent head d9cccd5. Consider uploading reports for the commit d9cccd5 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3810      +/-   ##
==========================================
- Coverage   85.74%   85.33%   -0.41%     
==========================================
  Files         951      954       +3     
  Lines      162837   163049     +212     
==========================================
- Hits       139620   139139     -481     
- Misses      23217    23910     +693     

[WenyXu]

@fengjiachun @MichaelScofield PTAL

[fengjiachun]

Almost LGTM

[MichaelScofield]

Just lock the sink table name and we are good to go.