[Modules] Fix roleAssignments naming and missing rename

[MariusStorhaug]

Description

• 100 renames of _rbac -> _roleAssignments
• 1 rename of file nested_rbac.bicep -> nested_roleAssignments.bicep
• 1 doc update covering the above

Pipeline references

Pipeline

Type of Change

Please delete options that are not relevant.

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Update to documentation

Checklist

• I'm sure there are no other open Pull Requests for the same update/change
• My corresponding pipelines / checks run clean and green without any errors or warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (readme)
• I did format my code