feat: further simplify the config for autogenerated Route host in OCP

[tumido]

Description of the change

In the current setup, the user needs to modify the default values to get proper backend-frontend routing. Let's simplify this for users using OCP router that can autogenerate hostname. This way the user needs to change/specify the `apps.

Existing or Associated Issue(s)

Resolves: #72

Additional Information

As a result, if user uses the default OpenShift autogenerated route host they can now use following values:

Old

upstream:
  backstage:
    appConfig:
      app:
        baseUrl: 'https://{{- print .Release.Name "-" .Release.Namespace -}}.apps.example.com'
      backend:
        baseUrl: 'https://{{- print .Release.Name "-" .Release.Namespace -}}.apps.example.com'
        cors:
          origin: 'https://{{- print .Release.Name "-" .Release.Namespace -}}.apps.example.com'

New

global:
  clusterRouterBase: apps.example.com

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.

[tumido]

CI is failing because of janus-idp/backstage-showcase#287

[schwesig]

/lgtm
/approve
side note: I am fine with the naming.