Simpler instruction in case of pg_upgrade failure

There are many cases (database had bad shutdown, missing locale env)
where the manual export isn't needed, so point the admin to meta so
some easier solutions can be tried first.

templates/postgres.template.yml

@@ -91,38 +91,10 @@ run:
            echo -------------------------------------------------------------------------------------
            echo UPGRADE OF POSTGRES FAILED
            echo
-           echo You are going to need to export your data and import into a clean instance:
+           echo Please visit https://meta.discourse.org/t/postgresql-12-update/151236 for support
            echo
-
-           if [ "$PG_MAJOR_OLD" = "10" ]; then
-             echo 'In containers/app.yml: Change "templates/postgres.template.yml" TO "templates/postgres.10.template.yml"'
-             echo
-           fi
-
-           echo Run "./launcher rebuild app" again
-           echo
-           echo When your instance is running:
-           echo Run "./launcher enter app"
-           echo "Run apt-get remove postgresql-client-10 && apt-get install postgresql-client-12"
-           echo Run "cd /shared/postgres_backup && sudo -u postgres pg_dump discourse > backup.db"
-           echo
-
-           if [ "$PG_MAJOR_OLD" = "10" ]; then
-             echo Undo the base_image in your container config
-           fi
-
-           echo Run: "./launcher stop app"
-           echo Run: "sudo mv /var/discourse/shared/standalone/postgres_data /var/discourse/shared/standalone/postgres_data_old"
-           echo Run: "./launcher rebuild app"
+           echo You can run "./launcher start app" to restart your app in the meanwhile
            echo
-           echo Run: "./launcher enter app"
-           echo Run: "cd /shared/postgres_backup"
-           echo Run: "sv stop unicorn"
-           echo Run: "sudo -iu postgres dropdb discourse"
-           echo Run: "sudo -iu postgres createdb discourse"
-           echo Run: "sudo -iu postgres psql discourse < backup.db"
-           echo Run: "exit"
-           echo Run: "./launcher rebuild app"
            exit 1
          fi