[DPE-4757] - Update shared library code, so that mongos waits for upg…

…rade (#430)

## Context - What is this file?
This library code is used between `mongos`-charm and `mongodb`-charm
(when Charmed MongoDB is running as a config-server), to manage
connections between routers and config-servers. In this lib:
- Charmed mongos requests the user and shares its user with its
associated client application
- Charmed mongos manages its connection with the associated
config-server
- Charmed mongos starts its `mongos` service (as it is required to have
a config-server before starting)

This file is "owned" by Charmed MongoDB - so any direct changes to the
file **must** be made in this repo, before copying them over to Charmed
Mongos

## Issue
`mongos` does not wait for upgrades to finish before processing
integrations to the `config-server`. To prevent any broken states, we
should finish an upgrade before integrating to the config-server.

## Solution
Check if an upgrade is on-going. If it is prevent the relevant hook from
executing.

## What is next
Update the `mongos` charm to have the newest version of this lib to
ensure that `mongos` waits for upgrades to finish before

charm_internal_version

@@ -1 +1 @@
-9
+10

lib/charms/mongodb/v0/config_server_interface.py

@@ -42,7 +42,8 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 6
+
+LIBPATCH = 7
 
 
 class ClusterProvider(Object):
@@ -240,6 +241,13 @@ def __init__(
         )
 
     def _on_database_created(self, event) -> None:
+        if self.charm.upgrade_in_progress:
+            logger.warning(
+                "Processing client applications is not supported during an upgrade. The charm may be in a broken, unrecoverable state."
+            )
+            event.defer()
+            return
+
         if not self.charm.unit.is_leader():
             return
 
@@ -286,6 +294,7 @@ def _on_relation_changed(self, event) -> None:
             return
 
         self.charm.status.set_and_share_status(ActiveStatus())
+        self.charm.mongos_intialised = True
 
     def _on_relation_broken(self, event: RelationBrokenEvent) -> None:
         # Only relation_deparated events can check if scaling down
@@ -339,6 +348,13 @@ def pass_hook_checks(self, event):
             event.defer()
             return False
 
+        if self.charm.upgrade_in_progress:
+            logger.warning(
+                "Processing client applications is not supported during an upgrade. The charm may be in a broken, unrecoverable state."
+            )
+            event.defer()
+            return False
+
         return True
 
     def is_mongos_running(self) -> bool: