[Backport 2.x] Changing XContentType to Media Type

[joshpalis]

Description

Manual Backport of #436

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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]

Codecov Report

Merging #440 (2e9309e) into 2.x (ebb56ce) will not change coverage.
Report is 1 commits behind head on 2.x.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                2.x     #440   +/-   ##
=========================================
  Coverage     29.19%   29.19%           
  Complexity       98       98           
=========================================
  Files            22       22           
  Lines          1185     1185           
  Branches        109      109           
=========================================
  Hits            346      346           
  Misses          818      818           
  Partials         21       21           

Files Changed	Coverage Δ
...rg/opensearch/jobscheduler/JobSchedulerPlugin.java	31.66% <ø> (ø)
...arch/jobscheduler/model/ExtensionJobParameter.java	0.00% <ø> (ø)
.../org/opensearch/jobscheduler/model/JobDetails.java	0.00% <ø> (ø)
...scheduler/rest/action/RestGetJobDetailsAction.java	42.59% <ø> (ø)
...ch/jobscheduler/rest/action/RestGetLockAction.java	34.69% <ø> (ø)
...obscheduler/rest/action/RestReleaseLockAction.java	11.11% <ø> (ø)
...obscheduler/rest/request/GetJobDetailsRequest.java	45.16% <ø> (ø)
...rg/opensearch/jobscheduler/sweeper/JobSweeper.java	39.74% <ø> (ø)
...rch/jobscheduler/transport/AcquireLockRequest.java	54.76% <ø> (ø)
...ch/jobscheduler/transport/AcquireLockResponse.java	0.00% <ø> (ø)
... and 6 more