Add json marshaling tests for action usage and OIDC types

[rameshgkwd05]

This PR covers JSON marshalling testing for following types (partial fix for #55)

1. actions_oidc

   1. type OIDCSubjectClaimCustomTemplate

2. actions_cache

   1. type ActionsCache
   2. type ActionsCacheList
   3. type ActionsCacheUsage
   4. type ActionsCacheUsageList
   5. type TotalCacheUsage
   6. (type ActionsCacheListOptions does not have any json encoding so we have skipped test case for it.)

NOTE for reviewers: This contribution is for hactoberfest credit please label it so. Thanks!

[rameshgkwd05]

Newly added tests are running fine locally

[codecov]

Codecov Report

Merging #2944 (fc3e7b5) into master (d99d3df) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2944   +/-   ##
=======================================
  Coverage   98.19%   98.19%           
=======================================
  Files         145      145           
  Lines       12720    12720           
=======================================
  Hits        12490    12490           
  Misses        156      156           
  Partials       74       74           

[gmlewis]

Thank you, @rameshgkwd05 !
LGTM.
Merging.