feat(coderd): refactors github pr sync functionality (#22715)

- Adds `_API_BASE_URL` to `CODER_EXTERNAL_AUTH_CONFIG_`
- Extracts and refactors existing GitHub PR sync logic to new packages
`coderd/gitsync` and `coderd/externalauth/gitprovider`
- Associated wiring and tests

Created using Opus 4.6

coderd/database/querier.go

@@ -39,6 +39,7 @@ type sqlcQuerier interface {
 	// multiple provisioners from acquiring the same jobs. See:
 	// https://www.postgresql.org/docs/9.5/sql-select.html#SQL-FOR-UPDATE-SHARE
 	AcquireProvisionerJob(ctx context.Context, arg AcquireProvisionerJobParams) (ProvisionerJob, error)
+	AcquireStaleChatDiffStatuses(ctx context.Context, limitVal int32) ([]AcquireStaleChatDiffStatusesRow, error)
 	// Bumps the workspace deadline by the template's configured "activity_bump"
 	// duration (default 1h). If the workspace bump will cross an autostart
 	// threshold, then the bump is autostart + TTL. This is the deadline behavior if
@@ -60,6 +61,7 @@ type sqlcQuerier interface {
 	// Only unused template versions will be archived, which are any versions not
 	// referenced by the latest build of a workspace.
 	ArchiveUnusedTemplateVersions(ctx context.Context, arg ArchiveUnusedTemplateVersionsParams) ([]uuid.UUID, error)
+	BackoffChatDiffStatus(ctx context.Context, arg BackoffChatDiffStatusParams) error
 	BatchUpdateWorkspaceAgentMetadata(ctx context.Context, arg BatchUpdateWorkspaceAgentMetadataParams) error
 	BatchUpdateWorkspaceLastUsedAt(ctx context.Context, arg BatchUpdateWorkspaceLastUsedAtParams) error
 	BatchUpdateWorkspaceNextStartAt(ctx context.Context, arg BatchUpdateWorkspaceNextStartAtParams) error