refactor(database): move hook logic into separate package

[jbrockopp]

Based off of https://github.com/go-vela/server/pull/574, https://github.com/go-vela/server/pull/663, https://github.com/go-vela/server/pull/687 and https://github.com/go-vela/server/pull/692

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

[codecov[bot]]

Codecov Report

Merging #721 (6b87304) into main (74d2a68) will decrease coverage by 0.18%. The diff coverage is 78.23%.

@@            Coverage Diff             @@
##             main     #721      +/-   ##
==========================================
- Coverage   54.59%   54.40%   -0.19%     
==========================================
  Files         216      224       +8     
  Lines       16178    16168      -10     
==========================================
- Hits         8832     8797      -35     
- Misses       6962     6978      +16     
- Partials      384      393       +9     

Impacted Files	Coverage Δ
api/hook.go	0.00% <0.00%> (ø)
api/webhook.go	0.00% <0.00%> (ø)
database/postgres/build.go	95.86% <ø> (ø)
database/sqlite/build.go	95.86% <ø> (ø)
database/hook/hook.go	51.72% <51.72%> (ø)
database/hook/last_repo.go	70.83% <70.83%> (ø)
database/hook/list.go	72.72% <72.72%> (ø)
database/sqlite/sqlite.go	64.70% <72.72%> (+1.26%)	:arrow_up:
database/postgres/postgres.go	65.06% <76.92%> (+1.49%)	:arrow_up:
database/hook/list_repo.go	79.06% <79.06%> (ø)
... and 13 more