Refactor custom AWS endpoint resolver

[kishorj]

Issue

Description

Refactor the custom aws endpoint resolver code to parse the --aws-api-endpoints flag to a string map instead of having custom code for the parsing. This will simplify the implementation.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[codecov-commenter]

Codecov Report

Merging #2270 (2cfd142) into main (79fdb7f) will decrease coverage by 0.15%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #2270      +/-   ##
==========================================
- Coverage   53.55%   53.40%   -0.16%     
==========================================
  Files         136      136              
  Lines        7607     7582      -25     
==========================================
- Hits         4074     4049      -25     
- Misses       3217     3218       +1     
+ Partials      316      315       -1     

Impacted Files	Coverage Δ
pkg/aws/endpoints/resolver.go	75.00% <0.00%> (-18.94%)	⬇️

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[M00nF1sh]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kishorj, M00nF1sh

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