feat(waf): add new check waf_global_rulegroup_not_empty

[HugoPBrito]

Context

AWS WAF Classic global rule groups allow you to manage multiple web access rules in a unified structure, providing better scalability and simplified security management. By grouping multiple rules, administrators can apply comprehensive security controls to monitor and filter web traffic based on predefined conditions. Having at least one rule within a rule group is necessary for ensuring that web traffic is effectively inspected and that appropriate actions are taken on requests, such as allowing, blocking, or counting them.

Description

This check verifies that AWS WAF Classic global rule groups contain at least one rule. If no rules are present, the group does not perform any inspection of web traffic, potentially allowing all traffic to pass unchecked.

Checklist

• Are there new checks included in this PR? Yes.
  • If so, do we need to update permissions for the provider? No.
• 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

Attention: Patch coverage is 90.00000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 89.46%. Comparing base (23a20a5) to head (085265c).

Files with missing lines	Patch %	Lines
prowler/providers/aws/services/waf/waf_service.py	87.50%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5467      +/-   ##
==========================================
+ Coverage   89.45%   89.46%   +0.01%     
==========================================
  Files        1059     1061       +2     
  Lines       32855    32928      +73     
==========================================
+ Hits        29390    29459      +69     
- Misses       3465     3469       +4     

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