internal/controller: support custom atlas.hcl

[datdao]

What does this PR do?

This PR introduces support for new methods of injecting atlas.hcl definitions, providing greater flexibility in specifying configurations. The following features are now supported:

• Inline Block Configuration

spec:
  envName: "example"
  config: |
    env "example" {
        lint {

        }
    }

• Configuration from a Secret

spec:
  envName: "example"
  configFrom:
    secretKeyRef:
        name: schema-config
        key: config.hcl

• Variables from secret/configmap

spec:
  envName: "example"
  vars:
    - name: db_url
      value: "localhost"
    - name: db_url_from_secret
      valueFrom:
        secretKeyRef:
          name: schema-config
          key: db_url
    - name: db_url_from_configmap
      valueFrom:
        configMapKeyRef:
          name: schema-config
          key: db_url
  config: |
    variable "db_url" {}
    env "example" {
      url = var.db_url
    }

Limitations

• Lint values that contain expressions are not yet supported in atlas.hcl.
• Configurations involving multiple targets in atlas.hcl are currently not supported.

[giautm]

Write more complicated tests: Use Getenv, datasource for load token,