feat: Adds postgres support

[soluchok]

Postgres support was removed from Trillian. See google/trillian#2432.
In this PR I copied everything they have + fixed it according to the latest changes.
Also, PR includes builds for log-server and log-signer.

Signed-off-by: Andrii Soluk [email protected]

[codecov-commenter]

Codecov Report

Merging #37 (42c7034) into main (1f29038) will decrease coverage by 1.33%.
The diff coverage is 83.60%.

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
- Coverage   86.45%   85.11%   -1.34%     
==========================================
  Files           8       13       +5     
  Lines         893     1693     +800     
==========================================
+ Hits          772     1441     +669     
- Misses         77      147      +70     
- Partials       44      105      +61     

Impacted Files	Coverage Δ
pkg/storage/postgres/provider.go	76.47% <76.47%> (ø)
pkg/storage/postgres/queue.go	77.27% <77.27%> (ø)
pkg/storage/postgres/log_storage.go	80.68% <80.68%> (ø)
pkg/storage/postgres/admin_storage.go	86.74% <86.74%> (ø)
pkg/storage/postgres/tree_storage.go	89.80% <89.80%> (ø)
cmd/vct/startcmd/start.go	84.33% <100.00%> (+0.24%)	⬆️
... and 2 more

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[bstasyszyn]

At one point maybe we should consider adding PostGreSQL support to the google/trillian project. It will be difficult to get latest bug fixes/features with a copy.