Generalize block available time metric for PeerDAS

[dapplion]

Currently BlockDelays metrics track all_blobs_observed which is has the "intention" to track the time at which the last blob for a block was received. This metric won't register for PeerDAS.

Proposed solution

To generalize this for PeerDAS

• Register the last blob or data column seen on all_blobs_observed

But we may want to do something different. Some early work

• Generalize block available time metric for PeerDAS #6850