fix: webhook race condition on hook creation

[jbrockopp]

xref: go-vela/community#997

Currently, there is an inconvenient bug that our users experience when Vela processes a webhook:

{"error":"unable to create webhook OrgName/RepoName/BuildNumber: ERROR: duplicate key value violates unique constraint \"hooks_repo_id_number_key\" (SQLSTATE 23505)"}

This errors happens when we attempt to create a hook in the database that contains the same number and repo_id.

This attempts to resolve that issue by creating a retry loop with backoff that will repeat the following operations:

• capture the last hook for the repo
• set fields on the new hook object to be created in the database
• create the webhook object in the database

Example

For the sake of discussion, I find examples helpful so let's say we have a repo where the last hook number is 10.

Using the example provided in the ticket, let's say we have two push events fire after a PR is merged:

• a push to the target branch for the PR
• a push for the deletion event of the source branch from the PR

In this scenario, the Vela server would process each event concurrently and attempt to insert a 11 hook record but one of these webhooks will fail to be processed due to the conflict as displayed above. This resolves that issue because in that scenario, we'd fall back to looking up the last hook for the repo (11) and updating the number to 12.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 30 lines in your changes missing coverage. Please review.

Project coverage is 52.81%. Comparing base (b998ec1) to head (b3d6ea7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
api/webhook/post.go	0.00%	30 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1175      +/-   ##
==========================================
- Coverage   52.84%   52.81%   -0.04%     
==========================================
  Files         551      551              
  Lines       19199    19211      +12     
==========================================
  Hits        10146    10146              
- Misses       8489     8501      +12     
  Partials      564      564              

Files with missing lines	Coverage Δ
api/webhook/post.go	0.00% <0.00%> (ø)

[plyr4]

sweet!