Mattermost 10.5.9 ESR release

[DavidePrincipi]

Update ns8-mattermost application with the upstream ESR release 10.5.9

Release Notes https://docs.mattermost.com/product-overview/mattermost-v10-changelog.html#release-v10-5-extended-support-release

[DavidePrincipi]

In Testing 2.2.2-dev.1

• Test update and new installation of Mattermost

[mrmarkuz]

Fresh install verified
Update verified

There's an error about search infrastructure but search is working so I think it can be ignored:

2025-08-04T09:39:39+02:00 [1:mattermost1:mattermost-app] error [2025-08-04 07:39:39.859 Z] failed to initialize search infrastructure    caller="app/plugin_api.go:1013" plugin_id=mattermost-ai error="search is disabled"