Allow a user to @mention all users with a particular custom attri

[aaronrothschild]

I don't want to mention a group, but all the people with a special attribute such as their timezone or interest. Kind of a dynamic at mention.

Perhaps when configuring each custom attribute the admin can optionally assign a name "handle" such as "@Timezone:PST" and the plugin intercepts that mention.

Issue created from a Mattermost message by @bcpg.

[Miseq]

Yea, it would be really usefull if I could add labels as "QA", "Dev", "Devops" to people and mention all of them on channel.