Decide enum for category in PII

[maririos]

See comment in : Azure/azure-sdk-for-java#13687 (comment)

When in PII we set domain... are those protected health information entities different than the ones in HealthCareEntity?
Does HealthCare has categories and different types?

[maririos]

https://github.com/Azure/azure-rest-api-specs-pr/pull/1728

[maririos]

PHI entities are unique to PII.
We decided to merge PHI and PII into the existing EntityCategory class as there are shared entities.