[MM-13746] Add GetTeamMembersForUser and GetChannelMembersForUser apis (#10269)

* Add GetTeamMembersForUser and GetChannelMembersForUser apis

* Address comments

* Fix tests

* Fix test

* Fix comment

* Fix minimum server version

* Change to []*model.ChannelMember

* Fix panic, add more tests

* Remove print statement

store/storetest/mocks/JSONSerializable.go

@@ -0,0 +1,26 @@
+// Code generated by mockery v1.0.0. DO NOT EDIT.
+
+// Regenerate this file using `make store-mocks`.
+
+package mocks
+
+import mock "github.com/stretchr/testify/mock"
+
+// JSONSerializable is an autogenerated mock type for the JSONSerializable type
+type JSONSerializable struct {
+	mock.Mock
+}
+
+// ToJson provides a mock function with given fields:
+func (_m *JSONSerializable) ToJson() string {
+	ret := _m.Called()
+
+	var r0 string
+	if rf, ok := ret.Get(0).(func() string); ok {
+		r0 = rf()
+	} else {
+		r0 = ret.Get(0).(string)
+	}
+
+	return r0
+}