Add slos for rekor v2 reads

[loosebazooka]

Add the slos for rekor reads.

[haydentherapper]

If this SLO is not met, will this trigger a page? If so, what's the action that an oncaller should take?

[loosebazooka]

Right, so merging this does nothing. I think what we need to do is allow a passthrough of the severity variable and then activate the slo so we control paging on the SLO module. I don't even know what kind of action an oncaller can take here -- gcs is down? our lb is down (is this even detected)?

[haydentherapper]

Yea, I'd like this to be a non-pageable SLO, so either just a dashboard or like you said, use severity to downgrade this to a warn.

[haydentherapper]

I'd mention "Read Availability" or something like that

[loosebazooka]

I'll go add the severity passthrough to slo first then.