feat: add Kubernetes secret resolver and documentation

[zofer1zohargo]

• Implement k8ssecret URL provider for reading DSN from Kubernetes secrets
• Support both full DSN and partial DSN with template placeholders (DSN_VALUE)
• Add comprehensive examples and documentation for k8s-secret usage
• Register k8ssecret provider in secret resolver
• Update main README to include Kubernetes secrets documentation
• Bump application version to 0.20.1 and chart appVersion

[zofer1zohargo]

Hi @burningalchemist,
I am not sure such developments can be handled.
I think I tried all options :-(
It is now in two PRs that need to be handled together, per your request.
We should really understand how to fix the CI to handle this case.
I assume that after approving the first one the second one should work but when I bump the appVersion I also need to submit the Chart.yaml which triggers a helm chart update.
No idea how you are handling it.
Waiting for your instructions

[burningalchemist]

Hey @zofer1zohargo, just remove all the helm stuff from the PR (Chart.yaml), leave only the go-related code as a feature for k8ssecret provider.

I'll do the release next week (so we have the container versions published), and with the separate pr we include the helm-related template changes and the rest.

This should work 🙌

P.S. Also, please revert VERSION file back to 0.20.0. The release version bump is done in a separate commit to tag and cut off the release. I'll handle it.

[zofer1zohargo]

Done. One day will get the hang of it :-)

[burningalchemist]

@zofer1zohargo Looks good, thanks! 🎉 Yeah, I'll tag you to demo the procedure. 🙌 I'll reply in the other PR shortly. 👍