Move SLE15 Stack Pipeline to GitHub Action

[fargozhu]

Is your feature request related to a problem? Please describe.

Currently the pipeline that triggers the pull request to update the SLE15 stack is on Concourse and we should move to GitHub Action to align with the KubeCF CI main strategy.

Describe the solution you'd like

Move to it's own GitHub Action.

Describe alternatives you've considered N/A

Additional context N/A

[fargozhu]

@viovanov @thardeck can you guys add more detailed information if needed so we can have this story in our next sprint?

[gaktive]

We need to bump the stack very soon tied to some older vulnerabilities reported in Trivi. Sounds like this will have to be manual for the interim.

[thardeck]

We need to bump the stack very soon tied to some older vulnerabilities reported in Trivi. Sounds like this will have to be manual for the interim.

This issue is not so urgent, since automation is already in place since some time, for example: https://github.com/cloudfoundry-incubator/kubecf/pull/1597

Parts of it are still running in Concourse, which is not ideal but not relevant for the issue you have mentioned.