Fix hardcoded region in cfn__resource_injection (Fixes #484)

[HoseinGhandi]

Description

This PR resolves Issue #484 by removing the hardcoded us-east-1 region within the cfn__resource_injection module, ensuring the tool functions correctly across all AWS regions.

Changes Made

• Removed the hardcoded 'us-east-1' string from the main function.
• Refactored get_session_from_key_name and get_aws_key_by_name to handle regions dynamically.
• Utilized **session_args to allow boto3.Session to intelligently default to the user's environment region or accept explicitly passed arguments.

Related Issue

Fixes #484

Thank you for reviewing! Let me know if any further modifications are needed.

[nobodynate]

@HoseinGhandi thank you for this pull request.
Is there a good reason to completely remove pacu/modules/cfn__resource_injection/main.py and pacu/modules/iam__privesc_scan/main.py?

[HoseinGhandi]

Hey @nobodynate, my bad! My Windows Antivirus falsely flagged those specific module files as malware and automatically deleted them from my local directory while I was working on the fix. I didn't notice the deletion got included in the commit! 😄
I've added an exclusion, restored the files, and updated the PR. Thanks for catching that!