fix(api): deprecate settings v2beta endpoints (#10909)

# Which Problems Are Solved

As part of our efforts to simplify the structure and versions of our
APIs, were moving all existing v2beta endpoints to v2 and deprecate
them. They will be removed in Zitadel V5.

# How the Problems Are Solved

- This PR deprecates all settings v2beta service and endpoints.
- The comments and have been improved and, where not already done, moved
from swagger annotations to proto.
- `LoginSettings`:
- `AllowUsernamePassword` has been deprecated and a corresponding
`AllowLocalAuthentication` has been introduced
- `SECOND_FACTOR_TYPE_OTP` has been deprecated and a
`SECOND_FACTOR_TYPE_TOTP` has been introduced as enum alias

# Additional Changes

- cleanups of some unused structs

# Additional Context

- part of https://github.com/zitadel/zitadel/issues/10772
- requires backport to v4.x

API_DESIGN.md

@@ -53,7 +53,7 @@ Please check out the structure Buf style guide for more information about the fo
 As a rule of thumb, redundant API methods are deprecated.
 
 - The proto option `grpc.gateway.protoc_gen_openapiv2.options.openapiv2_operation.deprecated` MUST be set to true.
-- One or more links to recommended replacement methods MUST be added to the deprecation message as a proto comment above the rpc spec.
+- One or more links to recommended replacement methods CAN be added to the deprecation message as a proto comment above the rpc spec.
 - Guidance for switching to the recommended methods for common use cases SHOULD be added as a proto comment above the rpc spec.
 
 #### Example