Fix documentation (actualized links to external resources) (#1929)

1) Changed link to kubernetes.io/docs due to movement article about pod's termination.
2) Changed link to kube-downscaler due to migration's project to codeberg.
3) Added parameter "pod_environment_secret" and small annotation.

Author: FactorT

docs/reference/operator_parameters.md

@@ -268,7 +268,7 @@ configuration they are grouped under the `kubernetes` key.
   will be used. The default is empty.
 
 * **pod_terminate_grace_period**
-  Postgres pods are [terminated forcefully](https://kubernetes.io/docs/concepts/workloads/pods/pod/#termination-of-pods)
+  Postgres pods are [terminated forcefully](https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle/#pod-termination)
   after this timeout. The default is `5m`.
 
 * **custom_pod_annotations**
@@ -290,7 +290,7 @@ configuration they are grouped under the `kubernetes` key.
   An array of annotations that should be passed from Postgres CRD on to the
   statefulset and, if exists, to the connection pooler deployment as well.
   Regular expressions like `downscaler/*` etc. are also accepted. Can be used
-  with [kube-downscaler](https://github.com/hjacobs/kube-downscaler).
+  with [kube-downscaler](https://codeberg.org/hjacobs/kube-downscaler).
 
 * **ignored_annotations**
   Some K8s tools inject and update annotations out of the Postgres Operator
@@ -412,6 +412,9 @@ configuration they are grouped under the `kubernetes` key.
   Postgres cluster. All variables from that ConfigMap are injected to the pod's
   environment, on conflicts they are overridden by the environment variables
   generated by the operator. The default is empty.
+  
+* **pod_environment_secret**
+  referencing secret with custom environment variables. The default is empty.
 
 * **pod_priority_class_name**
   a name of the [priority class](https://kubernetes.io/docs/concepts/configuration/pod-priority-preemption/#priorityclass)