Use bridge instead of per platform chatops?

Description

@sytses and I spoke with folks from matrix which is an open source standard for decentralised communication, providing simple HTTP APIs and open source reference implementations for securely distributing and persisting JSON over an open federation of servers, and Riot, which is a communication client built on top of matrix, about using their messaging protocol and integrating into GitLab. You can read the conversation in the internal partnership doc.

Implications

If we choose to integrate matrix with GitLab it will mean:

• Adding an in-between step that introduces complexity and confusion
• We'll need to add the Matrix Go SDK and all bridges to GitLab Omnibus
• We'll get support to all the communication platforms in one action
• It'll make it easy to add chat to GitLab itself later
• Easier to integrate with Gitter and IRC
• Solving the licensing concerns of Mattermost by making us flexible
• Not sure if we can use bots in our case but if we insist Matrix will add slash commands