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

console/src/app/components/features/features.component.ts

@@ -38,7 +38,6 @@ const FEATURE_KEYS = [
   'oidcTriggerIntrospectionProjections',
   'permissionCheckV2',
   'userSchema',
-  'webKey',
 ] as const;
 
 export type ToggleState = { source: Source; enabled: boolean };