Bump spilo and target version for PostgreSQL 15 (#2139)

* Bumped Spilo image tag to the one that supports PostgreSQL 15. Using CDP version temporarily until non-CDP one is released.
* Added support for PostgreSQL 15 and made it default. 9.5 and 9.6 are now no longer supported
* Bumped spilo image tag to 2.1-p9
* Bumped spilo image in test launcher

Co-authored-by: yoshihiko <ariyoshi10@gmail.com>
Co-authored-by: Felix Kunde <felix-kunde@gmx.de>

manifests/operatorconfiguration.crd.yaml

@@ -66,7 +66,7 @@ spec:
                   type: string
               docker_image:
                 type: string
-                default: "registry.opensource.zalan.do/acid/spilo-14:2.1-p7"
+                default: "ghcr.io/zalando/spilo-15:2.1-p9"
               enable_crd_registration:
                 type: boolean
                 default: true
@@ -168,7 +168,7 @@ spec:
                     default: "11"
                   target_major_version:
                     type: string
-                    default: "14"
+                    default: "15"
               kubernetes:
                 type: object
                 properties: