refactor GenerateResourceRequirements and provide unit tests

docs/reference/cluster_manifest.md

@@ -322,9 +322,7 @@ explanation of `ttl` and `loop_wait` parameters.
 
 Those parameters define [CPU and memory requests and limits](https://kubernetes.io/docs/concepts/configuration/manage-compute-resources-container/)
 for the Postgres container. They are grouped under the `resources` top-level
-key with subgroups `requests` and `limits`. The whole section is optional,
-however if you specify a request or limit you have to define everything
-(unless you are not modifying the default CRD schema validation). 
+key with subgroups `requests` and `limits`. 
 
 ### Requests
 

docs/reference/operator_parameters.md

@@ -159,9 +159,9 @@ Those are top-level keys, containing both leaf keys and groups.
   at the cost of overprovisioning memory and potential scheduling problems for
   containers with high memory limits due to the lack of memory on Kubernetes
   cluster nodes. This affects all containers created by the operator (Postgres,
-  Scalyr sidecar, and other sidecars except **sidecars** defined in the operator
-  configuration); to set resources for the operator's own container, change the
-  [operator deployment manually](https://github.com/zalando/postgres-operator/blob/master/manifests/postgres-operator.yaml#L20).
+  connection pooler, logical backup, scalyr sidecar, and other sidecars except 
+  **sidecars** defined in the operator configuration); to set resources for the
+  operator's own container, change the [operator deployment manually](https://github.com/zalando/postgres-operator/blob/master/manifests/postgres-operator.yaml#L20).
   The default is `false`.
 
 ## Postgres users