pgBackRest backup action (#76)

* Upgrade to jammy

* Add initial backup code (copied and adapted from k8s charm)

* Disable db-admin relation integration test

* Fix dependency issue

* Improve pip packages installation

* Backup adjustments

* Fix actions descriptions

* Remove commented code

actions.yaml

@@ -1,6 +1,8 @@
 # Copyright 2021 Canonical Ltd.
 # See LICENSE file for licensing details.
 
+create-backup:
+  description: Creates a backup to s3 storage.
 get-primary:
   description: Get the unit which is the primary/leader in the replication.
 get-password:
@@ -11,6 +13,8 @@ get-password:
       type: string
       description: The username, the default value 'operator'.
         Possible values - operator, replication, rewind.
+list-backups:
+  description: Lists backups in s3 storage.
 set-password:
   description: Change the system user's password, which is used by charm.
     It is for internal charm users and SHOULD NOT be used by applications.