Mobile push notifications are disabled after every time we ran `gitlab-ctl reconfigure`

Summary

Every time we run gitlab-ctl reconfigure Mattermost's config.js is overwritten and thus mobile push notifications settings are reset.

Steps to reproduce

Enable mobile push notifications via Mattermost's System Console, run gitlab-ctl reconfigure.

Expected behavior

Mobile push notifications are enabled.

Observed behavior

Mobile push notifications are disabled.

Possible fixes

I see several solutions for this problem:

• There should be a setting in /etc/gitlab/gitlab.rb corresponding to these settings so one can configure mobile push notifications permanently.
• gitlab-ctl reconfigure should be smart enough not to override the settings that have no corresponding records in /etc/gitlab/gitlab.rb.