feat(firehose): add new check firehose_stream_encrypted_at_rest

[HugoPBrito]

Context

Amazon Kinesis Data Firehose is a fully managed service for loading real-time streaming data into data lakes, data stores, and analytics services. For data security, AWS provides server-side encryption (SSE), which encrypts data at rest within the storage layer using keys from AWS Key Management Service (KMS). This ensures that any data written to Kinesis Firehose is encrypted before storage, helping to protect sensitive information and meet compliance standards.

Description

This check ensures that Amazon Kinesis Data Firehose delivery streams have server-side encryption enabled for data at rest. The check fails if a delivery stream is unencrypted, which means that the data stored within Firehose could be accessed without encryption safeguards.

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 95.12195% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.87%. Comparing base (3608aa3) to head (9ded480).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
...roviders/aws/services/firehose/firehose_service.py	90.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5635      +/-   ##
==========================================
- Coverage   89.91%   89.87%   -0.04%     
==========================================
  Files        1128     1130       +2     
  Lines       35180    35224      +44     
==========================================
+ Hits        31631    31659      +28     
- Misses       3549     3565      +16     

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