Consider adding an "On Hold" label

# 🚀 Feature Proposal #

We should consider adding an "On Hold" label that is distinct from the "Blocked" label. See the discussion in cisagov/skeleton-generic#63. It may even make sense to create both an "On Hold" label and a more specific "Waiting for Kraken" label.

## Motivation ##

When we are holding back a PR because we are waiting to gather enough PRs for a Kraken release, the PR is not "blocked" per se. There are also other cases where we might put a PR on hold even though it is not actually blocked by anything else, although perhaps the concept of a draft PR covers this case.

The advantage of creating a more specific "Waiting for Kraken" label is that we can easily do a search for it and thus identify all PRs that should be merged when it is time to release the Kraken.

Start by reading the discussion in cisagov/skeleton-generic#63 and reviewing the repository's existing label conventions. Determine whether the requested workflow needs an "On Hold" label, a "Waiting for Kraken" label, or both; done means the naming and intended distinction are agreed and the labels are added consistently.

Written by the indexing model from the issue text.