Resolve absolute references to the current fhir server similar to relative ones

[lmsurpre]

Is your feature request related to a problem? Please describe.
FHIR spec says that for a server at example.com, the following should be treated as equivalent:

<patient>
  <reference value="Patient/123"/>
</patient>

<patient>
  <reference value="http://example.org/fhir/Patient/123"/>
</patient>

Similarly, I think the following two search expressions should be equivalent:

Observation?patient=Patient/123

Observation?patient=http://example.org/fhir/Patient/123

Describe the solution you'd like
On the way in, we should detect absolute references to resources on the "current host" and normalize them to relative paths.

Describe alternatives you've considered
An alternative is to convert everything to an absolute URI, but thats a bigger departure from our status quo.

Additional context
Relates to discussions wrt enforcing referential integrity between resources.

[prb112]

This may exist already in #300 please confirm and add a test for this case

[prb112]

Team discussion: sprint 19 since the work is done

[prb112]

Moving to Review/QA.

@lmsurpre can you confirm? if not, move to Sprint 20

[lmsurpre]

Robin confirmed that with #1604 then this one will be resolved. When the full URL matches the URL of the fhir server, we strip off the URL prefix and store just the relative reference.