ci: Add GH action for running integration tests via ansible-collection-equinix

[t0mk]

This PR adds a GH action that will test metal-python PRs with integration tests from ansible-collectoin-equinix.

We clone the Ansible collection and then install metal-python version fetched from the PR. Then we run integration tests from Ansible collection.

This way we don't have to do an extra test suite for the generated Python SDK and we have some certainty that the relevant pieces of the generated code work.

It would be good to set User Agent for the Ansible calls. Right now it's not possible to do it over environment variables. We might need to implement settting UA over envvar in the Ansible collection.

For this to work, we also need METAL_API_TOKEN in secrets of this repo. Basically, the secrets and environments should be set just like in https://github.com/equinix-labs/ansible-collection-equinix.

@ctreatma what do you think?

[ctreatma]

Looks good to me at a glance. I'll run it post-merge and we can adjust if needed.

[ctreatma]

Manual trigger of the merged workflow failed: https://github.com/equinix-labs/metal-python/actions/runs/7280529360/job/19839134379#step:6:16

Now that the workflow is defined in main, you can run branch versions of the workflow without opening a PR in order to validate the workflow changes (workflow changes won't take effect for the PR itself because it's using the pull_request_target trigger, which uses the workflow file from the target branch).