Modify Enum conversions to be case-insensitive/case-correcting

[theunrepentantgeek]

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What this PR does / why we need it:

In some cases information returned about a resource is is inconsistent with the letter casing specified in the OpenAPI specs for a resource - for example, the specs might specify Succeeded but the service returns succeeded.

This PR modifies enum conversion to work in a case-insensitive way, which will case-correct values to conform with the OpenAPI specs.

Special notes for your reviewer:

The conversion from status to spec used by asoctl will also pick up this fix.

Closes #3805

How does this PR make you feel:

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 99.85577% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 53.70%. Comparing base (f66dd4e) to head (aa111dd). Report is 2 commits behind head on main.

Files	Patch %	Lines
...2/api/apimanagement/v1api20220801/api_types_gen.go	89.28%	3 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3880      +/-   ##
==========================================
+ Coverage   53.53%   53.70%   +0.16%     
==========================================
  Files        1523     1525       +2     
  Lines      550082   552819    +2737     
==========================================
+ Hits       294510   296878    +2368     
- Misses     210035   210392     +357     
- Partials    45537    45549      +12     

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