refactor(api): move log logic into separate package

[ecrupper]

Based off of #615 #754 #809 #828 #829 #847 #848 #849 #851 and #853

This change continues the refactor efforts initially introduced in the above PRs.

This adds a new log package to the github.com/go-vela/server/api package.

This contains all the same handlers that existed previously but with each of them within their own file.

Also changed GetBuildLogs to ListLogsForBuild to stay consistent.

[codecov]

Codecov Report

Merging #855 (a15a60f) into main (1884ca0) will increase coverage by 1.73%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #855      +/-   ##
==========================================
+ Coverage   63.10%   64.84%   +1.73%     
==========================================
  Files         285      284       -1     
  Lines       14944    14543     -401     
==========================================
  Hits         9430     9430              
+ Misses       5068     4667     -401     
  Partials      446      446