[Bug] Synced status doesn't update when no longer synced

Bug report

I'm not sure if this is actually a bug or if it's intended behavior, but either way the current behavior lessens the usefulness of the attribute.

Currently, the synced attribute for a subgraph only updates when a deployment reaches chainhead for the first time. It would be useful if it would be updated if it falls behind chainhead by a certain threshold, so it's easier to tell at a glance whether an allocation should be good to close or not. My ideal scenario would probably be the synced boolean being connected directly to a threshold number of blocks behind chainhead, with the threshold being configurable per chain. I could theoretically handle this myself using the blocks behind metric and some custom code, but it would be nice to have graph-node handle this if possible.

Relevant log output

No response

IPFS hash

No response

Subgraph name or link to explorer

No response

Some information to help us out

• Tick this box if this bug is caused by a regression found in the latest release.
• Tick this box if this bug is specific to the hosted service.
• I have searched the issue tracker to make sure this issue is not a duplicate.

OS information

None

No files, tests, logs, or implementation entry points are named. First locate the implementation of the subgraph synced attribute and clarify the per-chain threshold behavior; done means the status changes when a deployment falls behind chainhead and the threshold can be configured per chain.