Added "id" field support & policy validation tests

[nasir-rabbani]

1. Updated RuleId identifying regex to accept new id pattern (AC_PROVIDER_XXXX, where X denotes a digit).
2. Changed to Rule ID value in detailed report to id of metadata instead of reference_id
3. Added Policy validation test to perform below checks:
   • Required fields are not empty
   • reference_id and id follows the accepted pattern
   • Referenced rego files are present

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Merging #843 (180b857) into master (32a4c15) will decrease coverage by 0.07%.
The diff coverage is 45.00%.

@@            Coverage Diff             @@
##           master     #843      +/-   ##
==========================================
- Coverage   78.29%   78.22%   -0.08%     
==========================================
  Files         164      165       +1     
  Lines        4359     4376      +17     
==========================================
+ Hits         3413     3423      +10     
- Misses        730      735       +5     
- Partials      216      218       +2     

Impacted Files	Coverage Δ
pkg/policy/types.go	100.00% <ø> (ø)
pkg/utils/skip_rules.go	93.33% <ø> (ø)
pkg/policy/opa/engine.go	58.03% <28.57%> (-1.33%)	⬇️
pkg/policies/opa/rego/policy-test-util.go	42.85% <42.85%> (ø)
pkg/filters/filter-specs.go	87.09% <66.66%> (-5.22%)	⬇️
pkg/mapper/iac-providers/cft/mapper.go	93.89% <0.00%> (+3.05%)	⬆️

[patilpankaj212]

LGTM!!