cmd/k8s-operator,k8s-operator: allow users to configure proxy env vars via ProxyClass (#11743)

Adds new ProxyClass.spec.statefulSet.pod.{tailscaleContainer,tailscaleInitContainer}.Env field
that allow users to provide key, value pairs that will be set as env vars for the respective containers.
Allow overriding all containerboot env vars,
but warn that this is not supported and might break (in docs + a warning when validating ProxyClass).

Updates tailscale/tailscale#10709

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

cmd/k8s-operator/deploy/crds/tailscale.com_proxyclasses.yaml

@@ -177,6 +177,21 @@ spec:
                           description: Configuration for the proxy container running tailscale.
                           type: object
                           properties:
+                            env:
+                              description: List of environment variables to set in the container. https://kubernetes.io/docs/reference/kubernetes-api/workload-resources/pod-v1/#environment-variables Note that environment variables provided here will take precedence over Tailscale-specific environment variables set by the operator, however running proxies with custom values for Tailscale environment variables (i.e TS_USERSPACE) is not recommended and might break in the future.
+                              type: array
+                              items:
+                                type: object
+                                required:
+                                  - name
+                                properties:
+                                  name:
+                                    description: Name of the environment variable. Must be a C_IDENTIFIER.
+                                    type: string
+                                    pattern: ^[-._a-zA-Z][-._a-zA-Z0-9]*$
+                                  value:
+                                    description: 'Variable references $(VAR_NAME) are expanded using the previously defined environment variables in the container and any service environment variables. If a variable cannot be resolved, the reference in the input string will be unchanged. Double $$ are reduced to a single $, which allows for escaping the $(VAR_NAME) syntax: i.e. "$$(VAR_NAME)" will produce the string literal "$(VAR_NAME)". Escaped references will never be expanded, regardless of whether the variable exists or not. Defaults to "".'
+                                    type: string
                             resources:
                               description: Container resource requirements. By default Tailscale Kubernetes operator does not apply any resource requirements. The amount of resources required wil depend on the amount of resources the operator needs to parse, usage patterns and cluster size. https://kubernetes.io/docs/reference/kubernetes-api/workload-resources/pod-v1/#resources
                               type: object
@@ -305,6 +320,21 @@ spec:
                           description: Configuration for the proxy init container that enables forwarding.
                           type: object
                           properties:
+                            env:
+                              description: List of environment variables to set in the container. https://kubernetes.io/docs/reference/kubernetes-api/workload-resources/pod-v1/#environment-variables Note that environment variables provided here will take precedence over Tailscale-specific environment variables set by the operator, however running proxies with custom values for Tailscale environment variables (i.e TS_USERSPACE) is not recommended and might break in the future.
+                              type: array
+                              items:
+                                type: object
+                                required:
+                                  - name
+                                properties:
+                                  name:
+                                    description: Name of the environment variable. Must be a C_IDENTIFIER.
+                                    type: string
+                                    pattern: ^[-._a-zA-Z][-._a-zA-Z0-9]*$
+                                  value:
+                                    description: 'Variable references $(VAR_NAME) are expanded using the previously defined environment variables in the container and any service environment variables. If a variable cannot be resolved, the reference in the input string will be unchanged. Double $$ are reduced to a single $, which allows for escaping the $(VAR_NAME) syntax: i.e. "$$(VAR_NAME)" will produce the string literal "$(VAR_NAME)". Escaped references will never be expanded, regardless of whether the variable exists or not. Defaults to "".'
+                                    type: string
                             resources:
                               description: Container resource requirements. By default Tailscale Kubernetes operator does not apply any resource requirements. The amount of resources required wil depend on the amount of resources the operator needs to parse, usage patterns and cluster size. https://kubernetes.io/docs/reference/kubernetes-api/workload-resources/pod-v1/#resources
                               type: object