Updating GitLab Mattermost to 4.0 for GitLab 9.4 release

Mattermost 4.0 has been tested with GitLab SSO with official release on July 16 from https://about.mattermost.com/download/. Mattermost team is ready to test GitLab 9.4 omnibus RC for both upgrade and new install.

This MR has been updated for 4.0.1 released on July 18th.

Mattermost 4.0 includes a change when using Mattermost with a reverse proxy as noted here in May: https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2339.

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Key updates in this release:

• New look and default theme
• New Mattermost API v4 and integrations directory
• Italian language support

Full release notes can be found here. Changes to Mattermost config.json are documented in release notes.

There are security updates in Mattermost 4.0 affecting Team Edition so upgrading is recommended.

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Please let me know if you have any questions. Thanks!

unmarked as a Work In Progress

changed the description

@balasankarc Mattermost 4.0 is ready for GitLab 9.4 release.

Our team is ready to test Mattermost 4.0 on GitLab 9.4 omnibus RC for both upgrade and new install.

approved this merge request

assigned to @marin

merged

changed milestone to %9.5

mentioned in commit c89d0c47

@marin Is this added to GitLab 9.5 instead of 9.4?

Is there a concern from your end about adding Mattermost 4.0 to GitLab 9.4?

Sorry, I've placed a wrong milestone on the MR. It is going to be in 9.4.

changed milestone to %9.4

Good to hear, thanks @marin :)

mentioned in commit ee6f908f

mentioned in commit cd63e290