Switch to HTTP POST for FHIR Search Requests

[lincmba]

fixes #73

IMPORTANT: Where possible all PRs must be linked to a Github issue

Resolves [link to issue]

Engineer Checklist

• I have written Unit tests for any new feature(s) and edge cases for
  bug fixes
• I have added documentation for any new feature(s) and configuration
  option(s) on the README.md
• I have run mvn spotless:check to check my code follows the project's
  style guide
• I have run mvn clean test jacoco:report to confirm the coverage report
  was generated at plugins/target/site/jacoco/index.html
• I ran mvn clean package right before creating this pull request.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 46.15385% with 7 lines in your changes missing coverage. Please review.

Project coverage is 44.97%. Comparing base (712d495) to head (c11af54).
Report is 5 commits behind head on main.

Files	Patch %	Lines
...way/plugins/PractitionerDetailsEndpointHelper.java	44.44%	5 Missing ⚠️
...teway/plugins/LocationHierarchyEndpointHelper.java	66.66%	1 Missing ⚠️
.../fhir/gateway/plugins/PermissionAccessChecker.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #74      +/-   ##
============================================
- Coverage     45.01%   44.97%   -0.04%     
  Complexity      130      130              
============================================
  Files            16       16              
  Lines          1213     1225      +12     
  Branches        146      146              
============================================
+ Hits            546      551       +5     
- Misses          600      607       +7     
  Partials         67       67              

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[ndegwamartin]

Looks good to me, please add the version bump so that we tag for a release