Ensure auth.clientID is passed as string in Discord configuration

Discord client IDs are numeric (e.g. 12345).
Passing them as integers however, causes the Discord bridge's YAML parser
to parse them as integers and its config schema validation will fail.

Fixes #240 (Github Issue)

roles/matrix-bridge-appservice-discord/defaults/main.yml

@@ -69,7 +69,7 @@ matrix_appservice_discord_configuration_yaml: |
     disableJoinLeaveNotifications: false
   # Authentication configuration for the discord bot.
   auth:
-    clientID: {{ matrix_appservice_discord_client_id|string }}
+    clientID: {{ matrix_appservice_discord_client_id|string|to_json }}
     botToken: {{ matrix_appservice_discord_bot_token }}
   logging:
     # What level should the logger output to the console at.