Implement some channel endpoints for APIv4 (#5846)

* Add v4 endpoint for getting the channels on a team for a user

* Implement PUT /channels/{channel_id}/patch endpoint for APIv4

* Implement POST /teams/{team_id}/channels/search endpoint for APIv4

* Update permission check

model/channel_test.go

@@ -16,6 +16,39 @@ func TestChannelJson(t *testing.T) {
 	if o.Id != ro.Id {
 		t.Fatal("Ids do not match")
 	}
+
+	p := ChannelPatch{Name: new(string)}
+	*p.Name = NewId()
+	json = p.ToJson()
+	rp := ChannelPatchFromJson(strings.NewReader(json))
+
+	if *p.Name != *rp.Name {
+		t.Fatal("names do not match")
+	}
+}
+
+func TestChannelPatch(t *testing.T) {
+	p := &ChannelPatch{Name: new(string), DisplayName: new(string), Header: new(string), Purpose: new(string)}
+	*p.Name = NewId()
+	*p.DisplayName = NewId()
+	*p.Header = NewId()
+	*p.Purpose = NewId()
+
+	o := Channel{Id: NewId(), Name: NewId()}
+	o.Patch(p)
+
+	if *p.Name != o.Name {
+		t.Fatal("do not match")
+	}
+	if *p.DisplayName != o.DisplayName {
+		t.Fatal("do not match")
+	}
+	if *p.Header != o.Header {
+		t.Fatal("do not match")
+	}
+	if *p.Purpose != o.Purpose {
+		t.Fatal("do not match")
+	}
 }
 
 func TestChannelIsValid(t *testing.T) {