Add grafana annotation for phase in test-stack

[sh-cho]

Hi, I'm trying to test this project using test-stack locally and so far so good.
One thing is, it's hard to tell which phase currently is.

I can check container log, but I think it's more convenient to use Grafana annotation
Annotations can be created via grafana HTTP api

ex)

I might work on this if accepted

[softberries]

Hi @sh-cho, interesting idea, I'll investigate this