feat: ske-operator can optionally deploy the backstage controller

[kirederik]

Context

Customers of SKE should be able to automatically install the backstage controller as part of their helm installing the ske-operator. It should not be deployed by default.

Acceptance Criteria

Scenario: opt-in for deployment
Given I have set `backstageController: true` in my values file # or equivalent
When I "helm install" the ske-operator
Then the backstage controller is deployed

Scenario: not deployed by default
Given I have not set the backstage config in my values file
When I "helm install" the ske-operator
Then the backstage controller is not deployed

Engineering notes

• Learning from the past, let's ensure that the common configuration options (imagePullSecret, image, resource requests and limits, nodeAffinities, etc) are all configurable for the backstage controller deployment
• The chart should not deploy the backstage controller directly, but rather tell the ske-operator that it should deploy it.

Tasks

• New config props available for the backstage controller
• Backstage deployment is templated accordingly
• Update the docs