MM-10182 & MM-10183: Adds channel scheme and team scheme API endpoint. (#8680)

* MM-10183: Adds channel scheme API endpoint.

MM-10182: Adds team scheme API endpoint.

MM-10182_3: Switch from scheme_id in path to body.

* MM-10182/MM-10183: Changes path from 'schemes' to 'scheme'.

* MM-10182: Fix merge error.

app/channel_test.go

@@ -381,3 +381,21 @@ func TestAddChannelMemberNoUserRequestor(t *testing.T) {
 		assert.Equal(t, user.Username, post.Props["username"])
 	}
 }
+
+func TestAppUpdateChannelScheme(t *testing.T) {
+	th := Setup().InitBasic()
+	defer th.TearDown()
+
+	channel := th.BasicChannel
+	mockID := model.NewString("x")
+	channel.SchemeId = mockID
+
+	updatedChannel, err := th.App.UpdateChannelScheme(channel)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if updatedChannel.SchemeId != mockID {
+		t.Fatal("Wrong Channel SchemeId")
+	}
+}