CI: Combine conda and full testing into a single workflow

[akihironitta]

What does this PR do?

Addresses #14059.
Includes and closes #14565.

TODO

• Agree on the version matrix for testing
• Update docs
• Update checkgroup

Does your PR introduce any breaking changes? If yes, please list them.

None

Before submitting

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• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• [n/a] Did you write any new necessary tests? (not for typos and docs)
• [n/a] Did you verify new and existing tests pass locally with your changes?
• [n/a] Did you list all the breaking changes introduced by this pull request?
• [n/a] Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

PR review

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Did you have fun?

Make sure you had fun coding 🙃

cc @carmocca @akihironitta @Borda

[Borda]

It is intentional that all Azure configs are deleted?

[akihironitta]

It is intentional that all Azure configs are deleted?

Will revert the change! (I just didn't want to occupy the resources with the unrelated change in this PR)

[akihironitta]

As requested in #14059 (reply in thread), 114a4c0 added Python/PyTorch versions that were used in conda jobs. If there's no issue with all combinations here, this PR is ready.

@carmocca @awaelchli You've already left an approval, but please have another look if necessary.

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Conda installation testing will be added via #14374 independently of this PR.

The azure configs have been added back