MM-62782: Bumping minimum Postgres version to 13 (#30039)

As discussed in https://docs.mattermost.com/install/prepare-mattermost-database.html#minimum-supported-version-policy

https://mattermost.atlassian.net/browse/MM-62782

```release-note
Minimum postgres version has been bumped to 13.
```

Co-authored-by: Mattermost Build <build@mattermost.com>

server/build/docker-compose.common.yml

@@ -41,7 +41,7 @@ services:
     volumes:
       - ./docker/mysql.conf.d/replica.cnf:/etc/mysql/conf.d/mysql.cnf
   postgres:
-    image: "postgres:11"
+    image: "postgres:13"
     restart: always
     networks:
       - mm-test

server/build/docker-preview/Dockerfile

@@ -1,6 +1,6 @@
 # Copyright (c) 2016-present Mattermost, Inc. All Rights Reserved.
 # See License.txt for license information.
-FROM postgres:12
+FROM postgres:13
 
 RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 467B942D3A79BD29
 RUN apt-get update && apt-get install -y ca-certificates