`vouch_ready` is a prometheus metric that is `0` if Vouch is not yet
ready to validate, and `1` if it is.
`vouch_release` has a labeled value `version` that contains the release
version of Vouch.
This adds a label `epoch_slot` to the prometheus metric
`vouch_block_receipt_delay_seconds`. It has been noted that the receipt
delay is often significantly higher for the first (and, to a lesser
extent, second) slot in a given epoch. This allows the receipt delay to
be examined for specific slots in a given epoch.