Add acceptance test and guide for custom policy resource

[shobha2626]

1. What this PR does / why we need it: Add acceptance test and guide for custom policy resource

[codecov-commenter]

Codecov Report

Attention: 106 lines in your changes are missing coverage. Please review.

Comparison is base (d0d6414) 25.25% compared to head (da0f966) 25.29%.

Files	Patch %	Lines
...ces/policy/kind/custom/recipe/tmc_custom_schema.go	41.05%	56 Missing ⚠️
...ernal/resources/policy/kind/custom/input_schema.go	0.00%	31 Missing ⚠️
...ternal/resources/policy/kind/custom/spec_schema.go	0.00%	19 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #371      +/-   ##
==========================================
+ Coverage   25.25%   25.29%   +0.04%     
==========================================
  Files         191      192       +1     
  Lines       16532    16657     +125     
==========================================
+ Hits         4175     4214      +39     
- Misses      12139    12225      +86     
  Partials      218      218              

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[github-actions]

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