chore: add doc comments to server API

[haoqixu]

Add doc comments to server API.

[codecov]

Codecov Report

Attention: 129 lines in your changes are missing coverage. Please review.

Comparison is base (efddaa2) 76.11% compared to head (d4a2cd4) 72.43%.
Report is 30 commits behind head on main.

Files	Patch %	Lines
internal/certs.go	0.00%	118 Missing ⚠️
client/internal/httpsender.go	88.00%	2 Missing and 1 partial ⚠️
client/internal/mockserver.go	85.71%	2 Missing and 1 partial ⚠️
server/httpconnection.go	0.00%	2 Missing ⚠️
client/internal/clientcommon.go	90.90%	1 Missing ⚠️
client/internal/packagessyncer.go	0.00%	1 Missing ⚠️
server/serverimpl.go	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #215      +/-   ##
==========================================
- Coverage   76.11%   72.43%   -3.69%     
==========================================
  Files          24       25       +1     
  Lines        1834     2017     +183     
==========================================
+ Hits         1396     1461      +65     
- Misses        326      446     +120     
+ Partials      112      110       -2     

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[tigrannajaryan]

Thank you.