common: log endpoint in freshness checker

[saihaj]

Today indexers do not have a way to know what subgraph is "not fresh" this PR aims to introduce the endpoint of subgraph we consider is "not fresh" in the freshness checker

closes https://github.com/graphprotocol/indexer/issues/803

[fordN]

Hey sorry forgot to detail this before you submitted PR.

Would you mind altering commit format a bit to be consistent with past contributions on this repo? <package_name>: <Commit description>

Lately I've been shortening the package name to leave more room for description, so using common instead of indexer-common. * for something that applies to all packages.