supplement provisioning instructions

[davgordo]

I had a little trouble here and there with some gotchas in provisioning the demo, so adding the following clarifications:

• All branches of the shared workflow repo should be forked in order to include gh-pages for helm chart publishing.
• Documented some additional required steps to get the GitHub Actions for the Backstage image to build and publish properly. Also see the following PR that removes Kosli steps.
• Fixed Quay permissions image link
• Included additional required manual step to enable self-hosted runners for all repos
• Provided the user a workaround in case the Vault chart results in a TLS secret for the wrong service
• Instructed the user to initialize Vault, which must be done manually as far as I know

If I misinterpreted any of these additional provisioning requirements, please comment, I am happy to adjust the PR.

[raffaelespazzoli]

the "dummy" value is correct. that way the path operator can patch that value based on the actual cluster the to which those apps are being deployed.
Also let's remove kosli completely instead of documenting how to set it up.

[davgordo]

@raffaelespazzoli thanks for the review, I've modified the PR and submitted one for the backstage-app-demo repo.