Upgrade Mattermost and PostgreSQL

[stephdl]

Upgrade Mattermost and PostgreSQL to minor version

Proposed solution
Upgrade Mattermost to version 10.5.5 and PostgreSQL to version 17.5 to ensure security, performance improvements, and compatibility with upstream.

Alternative solutions
Keep current versions, but this may lead to missed updates and potential vulnerabilities.

Additional context
Refer to release notes of Mattermost 10.5.5 and PostgreSQL 17.5.

[stephdl]

QA

test with ghcr.io/nethserver/mattermost:2.2.1-dev.1

• case 1 direct install
  no issue expected
• case2 upgrade
  we upgrade to a minor version of mysql, the upgrade must be fine

[mrmarkuz]

Test case 1 verified

• Direct install works

Test case 2 verified

• Upgrade works