Update Mattermost to 7.9.1

What does this MR do?

Updates Mattermost to version 7.9.1

The full changelog for this release can be found here.

cc @amyblais @spirosoik @neil.barnett @jasonblais

Related issues

Test plan

Leveraged from !6275 (2faec4f3, comment 1068292590)

Testing Setup

I have DNS entries configured that point to a single virtual machine on my local network:

• gitlab.gitlab.MYDOMAIN.net
• mattermost.gitlab.MYDOMAIN.net

The machine spins up with a specified GitLab package installed and uses a minimal gitlab.rb:

external_url 'http://gitlab.MYDOMAIN.net'
mattermost_external_url 'http://mattermost.MYDOMAIN.net'

Package Testing Results

Common items

• All platforms built successfully on the dev server

Fresh Installation

• No issues with installation in the testing environment
• Verify mattermost version (/opt/gitlab/embedded/bin/mattermost version)
• Connected to gitlab.gitlab.MYDOMAIN.net
• Navigate to Admin>Settings>Network>Outbound requests and add mattermost.MYDOMAIN.net to Local IP addresses and domain names that hooks and services may address and click Save changes
• Navigate to mattermost.gitlab.MYDOMAIN.net
• Verified single-sign on using GitLab credentials is working
• Verified that when creating a group, checking the box for Create a Mattermost team for this group also creates a team in Mattermost and was able to join that team
• Created a test project within the group created in the previous step and initialized with a README
• Enabled slash commands using GitLab documentation
• Tested slash commands by creating a new issue from the Mattermost instance, after following prompt to re-authorize, the issue was successfully created
• Configured incoming web hooks for Mattermost using the GitLab Documentation
• Using the created web hook, followed documentation for adding notification support

Upgrade Installation

• Installed GitLab 15.10.x-ee
• Connected to gitlab.MYDOMAIN.net
• Navigate to Admin>Settings>Network>Outbound requests and add mattermost.MYDOMAIN.net to Local IP addresses and domain names that hooks and services may address and click Save changes
• Navigate to mattermost.MYDOMAIN.net
• Verified single-sign on using GitLab credentials is working
• Verified that when creating a group, checking the box for Create a Mattermost team for this group also creates a team in Mattermost and was able to join that team
• Created a test project within the group created in the previous step and initialized with a README
• Enabled slash commands using GitLab documentation
• Tested slash commands by creating a new issue from the Mattermost instance, after following prompt to re-authorize, the issue was successfully created
• Configured incoming web hooks for Mattermost using the GitLab Documentation
• Using the created web hook, followed documentation for adding followed documentation for adding notification support
• Upgraded to package with new Mattermost version
• Verify mattermost version (/opt/gitlab/embedded/bin/mattermost version)
• Tested slash commands and notification web hooks, they continued to work

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• Pipeline is green on dev.gitlab.org if the change is touching anything besides documentation or internal cookbooks
• trigger-package has a green pipeline running against latest commit

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for the GitLab Chart opened