[FHIR Core] Add the ability to sync using the custom endpoints definition on the Sync Config

[dubdabasoduba]

Describe the feature request.

• The OpenSRP 2.0 mobile application uses the Sync Config file to know what to sync down. It does so by allowing the definition of the resource types to sync down.
  • It also allows the definition of some search parameters.
• The proposed change is to update the mobile application to correctly Identify custom endpoints and handle them correctly when they are defined on Sync Config.
  • The custom endpoints do not require a /fhir after the base URL. The sync functionality on the app does not know how to handle switching between FHIR and Custom and endpoint request URL generation.

Acceptance criteria

• Be able to add the Custom endpoints to the sync config correctly retrieve data from the server

References

• https://docs.google.com/document/d/11Io0bMeQrEz4sdZYI4Qz-H4yRW8VYI-QJkNGt1qkiH4/edit?usp=sharing