MM-48186: Add a new API endpoint to add a user to their default GroupChannels and GroupTeams. (#21591)

* MM-48186: Add a new API endpoint to add a user to their default GroupChannels and GroupTeams.

* MM-48186: Removed unrelated lint fixes.

* MM-48186: Removed variable from previous iteration.

* MM-48186: Adds translation.

* MM-48186: Not upgrading golang.org/x/text in this pr.

* MM-48186: Validate user ID and auth service.

* MM-48186: Use user id from struct.

* MM-48186: Added basic client test.

* MM-48186: Adds empty translation.

* MM-48186: Added translations.

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/group.go

@@ -247,3 +247,11 @@ type GroupsWithCount struct {
 	Groups     []*Group `json:"groups"`
 	TotalCount int64    `json:"total_count"`
 }
+
+type CreateDefaultMembershipParams struct {
+	Since               int64
+	ReAddRemovedMembers bool
+	ScopedUserID        *string
+	ScopedTeamID        *string
+	ScopedChannelID     *string
+}