Initial commit for new 1.6 release with Postgres 13 support. (#1257)

* Initial commit for new 1.6 release with Postgres 13 support.
* Updating maintainers, Go version, Codeowners.
* Use lazy upgrade image that contains pg13.
* fix typo for ownerReference
* fix clusterrole in helm chart
* reflect GCP logical backup in validation
* improve PostgresTeam docs
* change defaults for enable_pgversion_env_var and storage_resize_mode
* explain manual part of in-place upgrade
* remove gsoc docs

Co-authored-by: Felix Kunde <felix-kunde@gmx.de>

manifests/complete-postgres-manifest.yaml

@@ -36,7 +36,7 @@ spec:
           defaultRoles: true
           defaultUsers: false
   postgresql:
-    version: "12"
+    version: "13"
     parameters:  # Expert section
       shared_buffers: "32MB"
       max_connections: "10"
@@ -93,9 +93,9 @@ spec:
       encoding: "UTF8"
       locale: "en_US.UTF-8"
       data-checksums: "true"
-    pg_hba:
-    - hostssl all all 0.0.0.0/0 md5
-    - host    all all 0.0.0.0/0 md5
+#    pg_hba:
+#      - hostssl all all 0.0.0.0/0 md5
+#      - host    all all 0.0.0.0/0 md5
 #    slots:
 #      permanent_physical_1:
 #        type: physical