Add GetChannelMember method to plugin API (#7930)

plugin/rpcplugin/api_test.go

@@ -54,6 +54,11 @@ func TestAPI(t *testing.T) {
 		Id: "thechannelid",
 	}
 
+	testChannelMember := &model.ChannelMember{
+		ChannelId: "thechannelid",
+		UserId:    "theuserid",
+	}
+
 	testTeam := &model.Team{
 		Id: "theteamid",
 	}
@@ -111,6 +116,11 @@ func TestAPI(t *testing.T) {
 		assert.Equal(t, testChannel, channel)
 		assert.Nil(t, err)
 
+		api.On("GetChannelMember", "thechannelid", "theuserid").Return(testChannelMember, nil).Once()
+		member, err := remote.GetChannelMember("thechannelid", "theuserid")
+		assert.Equal(t, testChannelMember, member)
+		assert.Nil(t, err)
+
 		api.On("CreateUser", mock.AnythingOfType("*model.User")).Return(func(u *model.User) (*model.User, *model.AppError) {
 			u.Id = "theuserid"
 			return u, nil