[MM-7968] restrict creation of direct channels to team members (#17222)

* restrict creation of direct channels to team members

* run make i18n-extract

* add suggestions from hahmadia

* place common-team-check logic in app layer

* use flat SQL query

* show more specific error message to user

* MM-7968: Fmt file.

* MM-7968: Fix for moved session field.

Co-authored-by: Max Erenberg <max.erenberg@mattermost.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Martin Kraft <martinkraft@gmail.com>
Co-authored-by: Martin Kraft <martin@upspin.org>

app/team.go

@@ -1016,6 +1016,14 @@ func (a *App) GetTeamMembersByIds(teamID string, userIDs []string, restrictions
 	return teamMembers, nil
 }
 
+func (a *App) GetCommonTeamIDsForTwoUsers(userID, otherUserID string) ([]string, *model.AppError) {
+	teamIDs, err := a.Srv().Store.Team().GetCommonTeamIDsForTwoUsers(userID, otherUserID)
+	if err != nil {
+		return nil, model.NewAppError("GetCommonTeamIDsForUsers", "app.team.get_common_team_ids_for_users.app_error", nil, err.Error(), http.StatusInternalServerError)
+	}
+	return teamIDs, nil
+}
+
 func (a *App) AddTeamMember(c *request.Context, teamID, userID string) (*model.TeamMember, *model.AppError) {
 	_, teamMember, err := a.AddUserToTeam(c, teamID, userID, "")
 	if err != nil {