chore(oidc): graduate webkey to stable (#10122)

# Which Problems Are Solved

Stabilize the usage of webkeys.

# How the Problems Are Solved

- Remove all legacy signing key code from the OIDC API
- Remove the webkey feature flag from proto
- Remove the webkey feature flag from console
- Cleanup documentation

# Additional Changes

- Resolved some canonical header linter errors in OIDC
- Use the constant for `projections.lock` in the saml package.

# Additional Context

- Closes #10029
- After #10105
- After #10061

cmd/start/start.go

@@ -550,7 +550,6 @@ func startAPIs(
 		keys.OIDC,
 		keys.OIDCKey,
 		eventstore,
-		dbClient,
 		userAgentInterceptor,
 		instanceInterceptor.Handler,
 		limitingAccessInterceptor,