Allow specific HTTP methods for core API endpoints

[oeyh]

Description

This PR updates data prepper server handlers to support proper HTTP methods specified in #313. Unit tests and docs are updated accordingly.

Issues Resolved

Resolves #313

Check List

• [x] New functionality includes testing.
• [x] New functionality has been documented.
  • [ ] New functionality has javadoc added
• [x] Commits are signed with a real name per the DCO

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov-commenter]

Codecov Report

Merging #1697 (3ccbc36) into main (caebb19) will increase coverage by 0.15%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##               main    #1697      +/-   ##
============================================
+ Coverage     93.18%   93.33%   +0.15%     
- Complexity     1332     1338       +6     
============================================
  Files           176      176              
  Lines          3917     3932      +15     
  Branches        312      315       +3     
============================================
+ Hits           3650     3670      +20     
+ Misses          193      188       -5     
  Partials         74       74              

Impacted Files	Coverage Δ
...aprepper/pipeline/server/ListPipelinesHandler.java	100.00% <100.00%> (ø)
...pper/pipeline/server/PrometheusMetricsHandler.java	100.00% <100.00%> (ø)
...h/dataprepper/pipeline/server/ShutdownHandler.java	100.00% <100.00%> (+66.66%)	:arrow_up:
.../org/opensearch/dataprepper/pipeline/Pipeline.java	88.57% <0.00%> (-4.29%)	:arrow_down:

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