feat: DISA Ubuntu 20.04 STIG compliance

[jadarsie]

Reason for Change:

Added feature flag to enforce the DISA Ubuntu 20.04 STIG. If this flag is set, extra OS configuration is applied on node provisioning in order to comply with the STIG.

• script cse_stig_ubuntu2004.sh fixes the findings found in "default" clusters
• the auditd rules are included in the VHD to save cloud-init space
• the e2e suite checks the findings are fixed

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[jadarsie]

/azp run

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