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.