Add: Validation for Policy Type

[BLasan]

fixes: https://github.com/wso2/api-manager/issues/2663

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 39.97%. Comparing base (6b0a6b6) to head (3f5fdec). Report is 8 commits behind head on master.

Files	Patch %	Lines
...isher/v1/impl/OperationPoliciesApiServiceImpl.java	0.00%	2 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #12371      +/-   ##
============================================
- Coverage     41.70%   39.97%   -1.73%     
- Complexity        0     3196    +3196     
============================================
  Files          1867     1867              
  Lines        137917   137923       +6     
  Branches      19936    19938       +2     
============================================
- Hits          57513    55131    -2382     
- Misses        73479    75748    +2269     
- Partials       6925     7044     +119     

Flag	Coverage Δ
integration_tests	32.36% <0.00%> (-3.04%)	:arrow_down:
unit_tests	20.04% <ø> (-0.02%)	:arrow_down:

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