[Feature request] - expose whether the node is synced in /v2/info

[hstove]

I've heard from a few different people that they'd like to have an easier way of answering the question "is my node synced with the network". One suggestion was to add this information to /v2/info, but I don't think that should be a requirement.

One thing I have noticed is that the prometheus metric stacks_node_stacks_tip_height isn't ever set until the node has finished syncing, so that does act as a kind of way to answer this question, but it would still be helpful to have other easier mechanisms.

It seems like you can answer this question by seeing if SortitionDB::get_canonical_stacks_chain_tip_hash returns an Ok, though I'm not sure.

[hstove]

Note from Jude: you can get this information from the network state machine. You want to check whether the p2p stack is in "initial block download" (IBD) mode.