feat(mito): preparation to implementing write

[evenyag]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

This PR adds utilities for implementing write for mito2, which mainly contains conversion between protobuf types and some validations.

• Imports an experimental greptime-proto that supports row insert requests
• Adds proto_util mod to help convert types between db and proto
• Validates and collects write requests in handle_write_requests. It use RegionWriteCtx to batch requests and maintains sequences
• Implements some validation for WriteRequest.
• Implements methods to fill columns by default value for WriteRequest

Checklist

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

Refer to a related PR or issue link (optional)

• Tracking issue for implementing mito as a region engine #1869
• Relies on refactor(mito): mv mito2 request #2086

[codecov]

Codecov Report

Merging #2085 (b47da8a) into develop (dda9225) will decrease coverage by 0.61%.
Report is 6 commits behind head on develop.
The diff coverage is 3.58%.

@@             Coverage Diff             @@
##           develop    #2085      +/-   ##
===========================================
- Coverage    85.23%   84.63%   -0.61%     
===========================================
  Files          683      686       +3     
  Lines       106960   107455     +495     
===========================================
- Hits         91171    90948     -223     
- Misses       15789    16507     +718     

[waynexia]

No test so I can only choose to believe the great coder