Help user to link multiple gitlab instances

Problem

If a user want to link to gitlab.com and gitlab.perso.com

Today solution

clone repo, change manifest id, recompile, add to mattermost, configure

Ideal solution

have list in plugin settings

Proposed solution

In CI we can :

• build normal bin
• change manifest id to add _2 at end and build
• change manifest id to add _3 at end and build
• change manifest id to add _4 at end and build
• upload all this version in realease tag

User can add enough instance of this plugin and configure them.

As mattermost do the job of isolation in KVStore and reducers all should work.