remove default azure credential

[liamlego]

Description

Removes DefaultAzureCredential usage and replaces with ManagedIdentityCredential

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (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)
• This change requires a documentation update

How Has This Been Tested?

Tested by deploying built image to pctasks and running workflow for chesepeake-lu

Checklist:

Please delete options that are not relevant.

• I have performed a self-review
• Changelog has been updated
• Documentation has been updated
• Unit tests pass locally (./scripts/test)
• Code is linted and styled (./scripts/format)