alarm logic for NTEnums

Currently there isn't any logic in `p4p_ext` for setting Enums to alarm on a specific index or choice. This is a common use case as Enums are often used as flags to indicate issues and therefore would want to be associated with an alarm state.

### Acceptance Criteria:
- [ ] new rule exists to handle enum alarm logic
- [ ] new rule is included in Enum related handlers if relevant
- [ ] methods are exposed to allow alarm configuration on Enum recipes
- [ ] config_parser knows how to deal with alarmed enums
- [ ] unit tests completed for new code
- [ ] integration tests for alarmed Enums

Start by tracing the existing alarm rules and Enum-related handlers in p4p_ext, then inspect config_parser to see how recipes are represented. Define the required Enum alarm configuration entry points and add unit tests plus integration tests for alarmed Enums. Done means the new rule is included where relevant and all listed acceptance criteria are covered.

Written by the indexing model from the issue text.