standby cluster that streams from a remote primary (#1830)

* add the possibility to create a standby cluster that streams from a remote primary
* extending unit tests
* add more docs and e2e test

Co-authored-by: machine424 <ayoubmrini424@gmail.com>

manifests/postgresql.crd.yaml

@@ -458,6 +458,17 @@ spec:
                     type: string
                   gs_wal_path:
                     type: string
+                  standby_host:
+                    type: string
+                  standby_port:
+                    type: string
+                oneOf:
+                - required:
+                  - s3_wal_path
+                - required:
+                  - gs_wal_path
+                - required:
+                  - standby_host
               streams:
                 type: array
                 nullable: true

manifests/standby-manifest.yaml

@@ -10,6 +10,8 @@ spec:
   numberOfInstances: 1
   postgresql:
     version: "14"
-# Make this a standby cluster and provide the s3 bucket path of source cluster for continuous streaming.
+  # Make this a standby cluster and provide either the s3 bucket path of source cluster or the remote primary host for continuous streaming.
   standby:
-    s3_wal_path: "s3://path/to/bucket/containing/wal/of/source/cluster/"
+    # s3_wal_path: "s3://mybucket/spilo/acid-minimal-cluster/abcd1234-2a4b-4b2a-8c9c-c1234defg567/wal/14/"
+    standby_host: "acid-minimal-cluster.default"
+    # standby_port: "5432"