Added Architecture Diagram

[wardbekker]

What this PR does / why we need it:

Added Loki Architecture Diagram

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Documentation added
• Tests updated

[owen-d]

LGTM, thanks!

@sandeepsukhani can you confirm we don't use the index cache from the ingesters anymore with boltdb-shipper?

[sandeepsukhani]

The diagram looks really good. Just a couple of feedbacks:

1. What does Q mean in the Ruler and Querier block?
2. I think we should point Compactor to the index store with both Read and Write arrows.
3. We support Redis as well for caching so maybe we should add that as well.

[owen-d]

The Q means the ruler embeds a querier as a subcomponent.

[sandeepsukhani]

The Q means the ruler embeds a querier as a subcomponent.

Ahh. Sorry, it was confusing to me. What do you folks think about removing it? I think it is more of an implementation detail but I do not strongly oppose keeping it.

@wardbekker The Q on the Ruler component looks a little out of alignment too. Can you please take care of it too if we decide to keep it?

[owen-d]

I think this is a good starter - we can improve in the future, but I dont' want to hold this up.