ci: switch to OIDC Federation for Azure

[adamconnelly]

Description of the change

Updating the packer build for Azure to use OIDC Federation instead of a static credential.

I've updated the CI build to have valid credentials for a service principal. This new SP has no access to anything - I've just added it to allow the packer validate step to work. I've also just hard-coded the client IDs into the actions on the grounds that they aren't credentials and don't need to be in secrets.

Type of change

• Bug fix (non-breaking change that fixes an issue);
• New feature (non-breaking change that adds functionality);
• Breaking change (fix or feature that would cause existing functionality to not work as expected);
• Documentation (a documentation or example fix not affecting the infrastructure managed by this module);
• Other;

Checklists

Development

• All necessary variables have been defined, with defaults if applicable;
• The HCL code is formatted;
• An AMI has been created in some AWS account, and the AMI is working as expected;

Code review

• This pull request has a descriptive title and information useful to a reviewer. There may be a screenshot or screencast attached;
• This pull request is no longer marked as "draft";
• Reviewers have been assigned;
• Changes have been reviewed by at least one other engineer;

[peterdeme]

👏