feat(api/user): add endpoint for viewing builds sent by current user

[ecrupper]

This would allow for the creation of a "Your Builds" page in the UI, which I think would be really convenient for our users.

Pretty slim related issue: go-vela/community#551

This query would be very taxing without introducing an index on sender for the builds table, which is the approach I took here.

[codecov]

Codecov Report

Merging #989 (3054bfe) into main (d90fdb7) will decrease coverage by 0.57%.
Report is 2 commits behind head on main.
The diff coverage is 30.00%.

@@            Coverage Diff             @@
##             main     #989      +/-   ##
==========================================
- Coverage   71.10%   70.53%   -0.57%     
==========================================
  Files         313      316       +3     
  Lines       13028    13207     +179     
==========================================
+ Hits         9263     9316      +53     
- Misses       3299     3421     +122     
- Partials      466      470       +4     

Files	Coverage Δ
database/build/count_sender.go	100.00% <100.00%> (ø)
database/build/index.go	42.85% <40.00%> (-4.21%)	⬇️
database/build/list_sender.go	79.54% <79.54%> (ø)
api/build/list_sender.go	0.00% <0.00%> (ø)

[ecrupper]

Closing this. I think we'll prefer dashboards over a page like this for the time being. May revisit at some point.