refactor: move dispatching logic into fhir-data-service, dry out code

[mcmcgrath13]

PULL REQUEST

Summary

Spin off/preparation PR from #3077. Refactor the fhir data service so the logic to do dispatching on source is in the service and not the route. Also simplify those db_getter functions so that they only do db getting and don't need to worry about mappings or wrangling params.

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.17%. Comparing base (163cbd2) to head (7acd790).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...-viewer/src/app/api/fhir-data/fhir-data-service.ts	94.11%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3130      +/-   ##
==========================================
+ Coverage   87.03%   89.17%   +2.13%     
==========================================
  Files         220       83     -137     
  Lines       13674     4248    -9426     
  Branches      714      715       +1     
==========================================
- Hits        11901     3788    -8113     
+ Misses       1764      451    -1313     
  Partials        9        9              

Flag	Coverage Δ
ecr-viewer	90.93% <94.73%> (-0.06%)	⬇️
fhir-converter	?
ingestion	?
message-parser	?
message-refiner	?
orchestration	85.67% <ø> (ø)
record-linkage	?
trigger-code-reference	?
validation	?

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Files with missing lines	Coverage Δ
...ntainers/ecr-viewer/src/app/api/fhir-data/route.ts	100.00% <100.00%> (ø)
...-viewer/src/app/api/fhir-data/fhir-data-service.ts	95.65% <94.11%> (-2.60%)	⬇️

... and 137 files with indirect coverage changes