Added mattermost config

[P4rcev4l]

Added config for the new mattermost-mobile app.
Tested locally.

I doubt it is an issue with the config but just in case:
Even though "author": "Mattermost" is set in com.mattermost.rn.json, it is only displayed for a split second in Obtainium before reverting to github.com as the author.

[ImranR98]

You don't need 3 separate variants here. Since the architecture string in each APK filename is identical to the strings Android would provide, Obtainium can automatically select the right APK to use (as long as the "Attempt to filter APKs..." toggle is enabled, which it is by default).

Even though "author": "Mattermost" is set in com.mattermost.rn.json, it is only displayed for a split second in Obtainium before reverting to github.com as the author.

Yes, overriding the author name is currently not supported (it will be in the next version 1.1.45 and then you shouldn't see this issue).

[P4rcev4l]

So we would like one config that that automatically selects the right APK and one for universal? Or is the first config enough?

[ImranR98]

One config is enough, no APK filter.