GraphQL (part 2): Model changes and resolvers (#19486)

This PR adds the necessary resolvers to support
the graphQL front-end. Some additional methods
need to be added to the model structs to support
this. Comments have been made to clarify their purpose.

There is a slight duplication of code in the api layer.
But eventually that's going to go away when we move
away from the REST API entirely.

The schema is in api4/schema.graphqls and gets compiled
into the binary as an asset.

The GraphiQL editor url is at GET /api/v5/graphql.

Everything is behind the feature flag MM_FEATUREFLAGS_GRAPHQL.

```release-note
NONE
```

api4/apitestlib.go

@@ -4,9 +4,12 @@
 package api4
 
 import (
+	"bytes"
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"math/rand"
 	"net"
@@ -19,6 +22,7 @@ import (
 	"time"
 
 	"github.com/gorilla/websocket"
+	graphql "github.com/graph-gophers/graphql-go"
 	s3 "github.com/minio/minio-go/v7"
 	"github.com/minio/minio-go/v7/pkg/credentials"
 	"github.com/stretchr/testify/require"
@@ -45,6 +49,7 @@ type TestHelper struct {
 
 	Context              *request.Context
 	Client               *model.Client4
+	GraphQLClient        *graphQLClient
 	BasicUser            *model.User
 	BasicUser2           *model.User
 	TeamAdminUser        *model.User
@@ -191,6 +196,7 @@ func setupTestHelper(dbStore store.Store, searchEngine *searchengine.Broker, ent
 	}
 
 	th.Client = th.CreateClient()
+	th.GraphQLClient = newGraphQLClient(fmt.Sprintf("http://localhost:%v", th.App.Srv().ListenAddr.Port))
 	th.SystemAdminClient = th.CreateClient()
 	th.SystemManagerClient = th.CreateClient()
 
@@ -374,6 +380,13 @@ func (th *TestHelper) TearDown() {
 	th.ShutdownApp()
 }
 
+func closeBody(r *http.Response) {
+	if r.Body != nil {
+		_, _ = io.Copy(ioutil.Discard, r.Body)
+		_ = r.Body.Close()
+	}
+}
+
 var initBasicOnce sync.Once
 var userCache struct {
 	SystemAdminUser   *model.User
@@ -768,10 +781,16 @@ func (th *TestHelper) CreateDmChannel(user *model.User) *model.Channel {
 
 func (th *TestHelper) LoginBasic() {
 	th.LoginBasicWithClient(th.Client)
+	if os.Getenv("MM_FEATUREFLAGS_GRAPHQL") == "true" {
+		th.LoginBasicWithGraphQL()
+	}
 }
 
 func (th *TestHelper) LoginBasic2() {
 	th.LoginBasic2WithClient(th.Client)
+	if os.Getenv("MM_FEATUREFLAGS_GRAPHQL") == "true" {
+		th.LoginBasicWithGraphQL()
+	}
 }
 
 func (th *TestHelper) LoginTeamAdmin() {
@@ -793,6 +812,13 @@ func (th *TestHelper) LoginBasicWithClient(client *model.Client4) {
 	}
 }
 
+func (th *TestHelper) LoginBasicWithGraphQL() {
+	_, _, err := th.GraphQLClient.login(th.BasicUser.Email, th.BasicUser.Password)
+	if err != nil {
+		panic(err)
+	}
+}
+
 func (th *TestHelper) LoginBasic2WithClient(client *model.Client4) {
 	_, _, err := client.Login(th.BasicUser2.Email, th.BasicUser2.Password)
 	if err != nil {
@@ -1251,3 +1277,22 @@ func (th *TestHelper) SetupScheme(scope string) *model.Scheme {
 	}
 	return scheme
 }
+
+func (th *TestHelper) MakeGraphQLRequest(input *graphQLInput) (*graphql.Response, error) {
+	url := fmt.Sprintf("http://localhost:%v", th.App.Srv().ListenAddr.Port) + model.APIURLSuffixV5 + "/graphql"
+
+	buf, err := json.Marshal(input)
+	if err != nil {
+		panic(err)
+	}
+
+	resp, err := th.GraphQLClient.doAPIRequest("POST", url, bytes.NewReader(buf), map[string]string{})
+	if err != nil {
+		panic(err)
+	}
+	defer closeBody(resp)
+
+	var gqlResp *graphql.Response
+	err = json.NewDecoder(resp.Body).Decode(&gqlResp)
+	return gqlResp, err
+}