MM-2954 - Add a separate post type for /me messages and update formatting (#11082)

* MM-2954

* Added new const post type for /me commands
* Modified me command to return response text without *__* wrapper
* Modified unit test for MeCommand to reflect changes
* Added unit test for the me command provider

* * Reverted change to text property in me command response
* Added original message in me command response props
* Updated unit tests

* gofmt changes

app/command_me_test.go

@@ -0,0 +1,27 @@
+package app
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/mattermost/mattermost-server/model"
+)
+
+func TestMeProviderDoCommand(t *testing.T) {
+	th := Setup(t).InitBasic()
+	defer th.TearDown()
+
+	mp := MeProvider{}
+
+	msg := "hello"
+
+	resp := mp.DoCommand(th.App, &model.CommandArgs{}, msg)
+
+	assert.Equal(t, model.COMMAND_RESPONSE_TYPE_IN_CHANNEL, resp.ResponseType)
+	assert.Equal(t, model.POST_ME, resp.Type)
+	assert.Equal(t, "*"+msg+"*", resp.Text)
+	assert.Equal(t, model.StringInterface{
+		"message": msg,
+	}, resp.Props)
+}