feat: allow serve json rpc request under grpc only mode

[mmsqe]

Description

for test info

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Author Checklist

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I have...

• tackled an existing issue or discussed with a team member
• left instructions on how to review the changes
• targeted the main branch

[codecov]

Codecov Report

❌ Patch coverage is 0% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.12%. Comparing base (cd4f406) to head (7e724dc).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
server/start.go	0.00%	27 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #826      +/-   ##
==========================================
+ Coverage   64.97%   65.12%   +0.15%     
==========================================
  Files         317      317              
  Lines       21607    21630      +23     
==========================================
+ Hits        14039    14087      +48     
- Misses       6348     6382      +34     
+ Partials     1220     1161      -59     

Files with missing lines	Coverage Δ
server/start.go	0.00% <0.00%> (ø)

... and 5 files with indirect coverage changes

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