refactor(repo): nested repository from server

[ecrupper]

Follow up from: go-vela/server#1095

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 81.65%. Comparing base (17a269b) to head (3cbad42).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #549   +/-   ##
=======================================
  Coverage   81.65%   81.65%           
=======================================
  Files         147      147           
  Lines        3603     3603           
=======================================
  Hits         2942     2942           
  Misses        485      485           
  Partials      176      176           

Files	Coverage Δ
action/pipeline/validate.go	87.82% <100.00%> (ø)
action/repo/add.go	89.47% <100.00%> (ø)
action/repo/table.go	100.00% <100.00%> (ø)
action/repo/update.go	94.73% <100.00%> (ø)
action/pipeline/exec.go	0.00% <0.00%> (ø)