[MM-57568] Synthetic user created from DM/GM have wrong RemoteID

[JulienTant]

Summary

When creating a synthetic user from a DM/GM, we set a remoteID based on the user UUID instead of using the plugin remoteID.

Example of how it's done for the syncUsers job: https://github.com/mattermost/mattermost-plugin-msteams/blob/main/server/plugin.go#L727

Ticket Link

https://mattermost.atlassian.net/browse/MM-57568

[JulienTant]

@lieut-data we do have this migration that runs everytime if the plugin has a remoteID:

func (s *SQLStore) runMigrationRemoteID(remoteID string) error {
    _, err := s.getQueryBuilder().Update("Users").Set("RemoteID", remoteID).Where(sq.And{
        sq.NotEq{"RemoteID": nil},
        sq.NotEq{"RemoteID": ""},
        sq.Expr("RemoteID NOT IN (SELECT remoteid FROM remoteclusters)"),
        sq.Like{"Username": "msteams_%"},
    }).Exec()
    return err
}

So anyone with a msteams_ name, that has a RemoteID AND this RemoteID is NOT part of remoteclusters will be assigned the plugin RemoteID. So in theory, every restart of the plugin """fixes""" the existing users.