Add SPM validation in each PR

[diegojerezba]

Proposed changes

This PR adds a new check in the pr-validation.yml. It consists in an integration of the changes of the current branch into the NativeAuth Sample App using a Swift Package.

These are the steps that are done:

• Creates MSAL.zip of the xcframework.
  • It configures the URL and the checksum so the Sample App will use the changes we want to test.
• Pushes it to a temporary branch.
• Clones the NativeAuth Sample App repo, and configures it to download the Swift Package from the temporary branch.
• Builds the Sample App.
• Cleans up.

Note: I have checked the build.py script and I think it's different enough from what we are trying to do here, so I thought it is better to have two separate jobs, even if both scripts build the framework. I'm open to discussion on this.

The time it takes the PR-validation hasn't been incremented, as it runs in parallel and this job takes ~6-10 min.

The following tests have been done:

• Test 1: (Pre)configure the sample app to use a new public method published in the current branch of MSAL.
• Test 2: Make a breaking change in MSAL, the Sample App shouldn't work.
• Test 3: If any build fails, the pipeline fails (and the temporary branch is deleted).
• Test 4: If for any reason the checksum calculation doesn't work, the pipeline fails (and the temporary branch is deleted).

Type of change

• [ ] Feature work
• [ ] Bug fix
• [ ] Documentation
• [ ] Engineering change
• [x ] Test
• [ ] Logging/Telemetry

Risk

• [ ] High – Errors could cause MAJOR regression of many scenarios. (Example: new large features or high level infrastructure changes)
• [x] Medium – Errors could cause regression of 1 or more scenarios. (Example: somewhat complex bug fixes, small new features)
• [ ] Small – No issues are expected. (Example: Very small bug fixes, string changes, or configuration settings changes)

[ameyapat]

Added a few comments. Otherwise, lgtm

[diegojerezba]

I'd suggest to manually run the pipeline on this branch as a sanity check

Done: https://identitydivision.visualstudio.com/IDDP/_build/results?buildId=1320628&view=results