fix: remove artifact-registry

[artemrys]

This PR removes artifact-registry step from the pipeline as we don't need Docker containers with add-on builds in the ghcr.io. It is not used in the infra anywhere. Also clean up README.md.

Test run: https://github.com/splunk/splunk-add-on-for-mysql/actions/runs/7669490177

[mkolasinski-splunk]

I think in existing @ajanus-splunk compatibility pipeline TA build is being downloaded from artifacts related with given workflow execution.
Worth confirming and taking under consideration when designing new solution

[artemrys]

I think in existing @ajanus-splunk compatibility pipeline TA build is being downloaded from artifacts related with given workflow execution. Worth confirming and taking under consideration when designing new solution

I don't think we are breaking this contract, artifact-registry uploads to GitHub Registry, not as workflow's artifact.

[kdoroszko-splunk]

I think we could also remove images/artifacts_all.png file and images/modinput/ directory.

[artemrys]

I think we could also remove images/artifacts_all.png file and images/modinput/ directory.

Let's do!

[srv-rr-github-token]

🎉 This PR is included in version 4.16.0 🎉

The release is available on GitHub release

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