fix: Always include the default app-config.yaml from the Backstage image in the container command

[rm3l]

Description of the change

As reported in #290, deploying the current Helm Chart might result in a Backstage pod not being able to start due to a config validation error. You can run this command from the main branch to reproduce the issue:

helm install my-backstage ./charts/backstage \
  --set backstage.appConfig.app.baseUrl=https://backstage.mydomain.com \
  --set backstage.appConfig.backend.baseUrl=https://backstage.mydomain.com

To fix this issue (and also prevent future similar issues), I thought it would make sense to include the default app-config.yaml file in the backstage-backend container command, just like it is currently done in the backstage Dockerfile.

Existing or Associated Issue(s)

Fixes #290

Additional Information

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md. The helm-docs utility can be used to generate the necessary content. Use helm-docs --dry-run to preview the content.
• JSON Schema generated.
• List tests pass for Chart using the Chart Testing tool and the ct lint command.

[rm3l]

/cc @ChrisJBurns Thoughts on this? This is confirmed to fix issues like #290
Thanks.

[ChrisJBurns]

@vinzscam Wondering what your thoughts are on this? I always defer to yourself when it comes to some of the app-config changes 😄