ci: implement docbot in cyborg

[tisonkun]

I hereby agree to the terms of the GreptimeDB CLA.

Refer to a related PR or issue link (optional)

What's changed and what's your intention?

This closes #3855. Let me test it out in the fork first.

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.

[tisonkun]

A few improvements can be made. Testing at tisonkun#4.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.34%. Comparing base (f16ce3c) to head (0f06875).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3937      +/-   ##
==========================================
- Coverage   85.79%   85.34%   -0.46%     
==========================================
  Files         965      971       +6     
  Lines      165107   166798    +1691     
==========================================
+ Hits       141654   142346     +692     
- Misses      23453    24452     +999     

[tisonkun]

Should be ready for review now.

[tisonkun]

cc @nicecui may you check this workflow makes sense to you.

[nicecui]

LGTM