feat(redshift): add new check redshift_cluster_non_default_username

[danibarranqueroo]

Context

This new check verifies that Amazon Redshift clusters do not use the default admin username "awsuser". Using a non-default username is crucial for reducing the risk of unauthorized access, as default usernames are well-known and often targeted by attackers.

Description

Added new check redshift_cluster_non_default_username with its unit tests.

Checklist

• Are there new checks included in this PR? Yes / No
  • If so, do we need to update permissions for the provider? Please review this carefully.
• Review if the code is being covered by tests.
• Review if code is being documented following this specification https://github.com/google/styleguide/blob/gh-pages/pyguide.md#38-comments-and-docstrings
• Review if backport is needed.

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.11%. Comparing base (77ac5e3) to head (56345f4).
Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5268      +/-   ##
==========================================
- Coverage   89.12%   89.11%   -0.01%     
==========================================
  Files         993      994       +1     
  Lines       30509    30528      +19     
==========================================
+ Hits        27191    27205      +14     
- Misses       3318     3323       +5     

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[MrCloudSec]

Good job!