BB2-3375: Refer FHIR resource in open api instead of creating schema

[stiwarisemanticbits]

JIRA Ticket: BB2-3375

What Does This PR Do?

1. Remove schema for FHIR resource and instead simply refer to them just like BFD
2. Remove unnecessary schema from error message and simply have description.

   What Should Reviewers Watch For?

If you're reviewing this PR, please check for these things in particular:

Validation

Copy paste openap.yaml contents in swager editor online https://editor.swagger.io/ to validate

What Security Implications Does This PR Have?

Please indicate if this PR does any of the following:

• Adds any new software dependencies

• Modifies any security controls

• Adds new transmission or storage of data

• Any other changes that could possibly affect security?

• [ ] Yes, one or more of the above security implications apply. This PR must not be merged without the ISSO or team security engineer's approval.

Any Migrations?

• [ ] Yes, there are migrations
  • [ ] The migrations should be run PRIOR to the code being deployed
  • [ ] The migrations should be run AFTER the code is deployed
  • [ ] There is a more complicated migration plan (downtime, etc)
• [x] No migrations