Refactor save service response object

[BobanL]

PULL REQUEST

Summary

• No longer return NextResponse from service since it's more difficult to read and handle in the service layer
• Do not return error messages in response since it may leak information (see a similar code scanning issue).
• Save both fhir bundle and metadata async
• Remove pool.close() since it isn't recommended.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.67%. Comparing base (89f3e8d) to head (ff6ddb9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3018      +/-   ##
==========================================
- Coverage   86.00%   85.67%   -0.34%     
==========================================
  Files         162       25     -137     
  Lines       10855     1424    -9431     
==========================================
- Hits         9336     1220    -8116     
+ Misses       1519      204    -1315     

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

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see 137 files with indirect coverage changes