[Aider assisted]: Use SelectBuilder and GetBuilder in webhook_store.go (#29555)

I was planning to kick off a campaign for this. But aider can do this just fine.

Starting off with a single file for now. But will slowly send more PRs with larger
commit diffs.

```release-note
NONE
```

Co-authored-by: Mattermost Build <build@mattermost.com>

.gitignore

@@ -157,3 +157,5 @@ docker-compose.override.yaml
 ## Notice Folders
 .notice/
 .notice-work/
+.aider*
+.env