✨ Support Application Credential auth

[apricote]

What this PR does / why we need it:

We currently require an explicit project_id field in the clouds.yaml. This conflicts with the usual fields for Application Credentials, as they already include a scope, and setting another conflicts with that.

In this commit, we instead save the returned project_id from the initial auth api call, and pass it around to all services using the Scope struct.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1146

Special notes for your reviewer:

1. Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

/hold

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[jichenjc]

/test all

[apricote]

/retest

Thanks for the extensive first round of review :) New commit with all requested changes is up.

[apricote]

/hold cancel

[seanschneeweiss]

Nice one.
/lgtm

[jichenjc]

@apricote not sure it's eligible to add some test cases (with application ID) later on?

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: apricote, jichenjc

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[apricote]

@apricote not sure it's eligible to add some test cases (with application ID) later on?

@jichenjc I had a unit test for the getProjectIDFromAuthResult, but couldn't figure out how to mock the token.CreateResult struct, if you have any guidance for that, I would gladly add a test case for this.

In general I would appreciate a test for this, that would probably mean to extend our e2e tests to use an addition clouds.yaml secret that uses application credentials. Are these supported by devstack?