Upgrade mautrix-gmessages (v0.4.3 -> v0.5.0) and adapt configuration

Related to:
- https://github.com/mautrix/gmessages/releases/tag/v0.5.0
- https://mau.fi/blog/2024-09-mautrix-release/

It seems like the new version does not support a `/metrics` endpoint.
We skip keep the Ansible variables, but they're not doing anything.

docs/configuring-playbook-bridge-mautrix-gmessages.md

@@ -14,14 +14,12 @@ matrix_mautrix_gmessages_enabled: true
 
 If you'd like to use [Double Puppeting](https://docs.mau.fi/bridges/general/double-puppeting.html) (hint: you most likely do), you have 2 ways of going about it.
 
-### Method 1: automatically, by enabling Appservice Double Puppet or Shared Secret Auth
+### Method 1: automatically, by enabling Appservice Double Puppet
 
-The bridge will automatically perform Double Puppeting if you enable the [Appservice Double Puppet](configuring-playbook-appservice-double-puppet.md) service or the [Shared Secret Auth](configuring-playbook-shared-secret-auth.md) service for this playbook.
+The bridge will automatically perform Double Puppeting if you enable the [Appservice Double Puppet](configuring-playbook-appservice-double-puppet.md) service for this playbook.
 
 Enabling [Appservice Double Puppet](configuring-playbook-appservice-double-puppet.md) is the recommended way of setting up Double Puppeting, as it's easier to accomplish, works for all your users automatically, and has less of a chance of breaking in the future.
 
-Enabling double puppeting by enabling the [Shared Secret Auth](configuring-playbook-shared-secret-auth.md) service works at the time of writing, but is deprecated and will stop working in the future.
-
 ### Method 2: manually, by asking each user to provide a working access token
 
 **Note**: This method for enabling Double Puppeting can be configured only after you've already set up bridging (see [Usage](#usage)).