Allow specifying since flag for Carp

[SebastienGllmt]

This is another change we want users to be able to specify in their config. Currently we pass since: None to Oura, but this should be configurable. The solution for this is going to be the same solution as the BearerKind ticket: #34

[SebastienGllmt]

We already have a start_block undocumented parameter in the main indexer crate so it may be good to formalize it

[bakon11]

Hi,

I tried using start block, but when I feed it a block that doesn't exist in the DB yet, it gives me an error saying that exactly.

Block hash does not exist in database

Is this flag only when you've already synced everything and want to sync extra data when changes to execution plan have been made?

Thanks.

[tdedgx]

upvote! I asked for something similar in discord spt not sure if you saw that. I still cant get it to start from a certain block, tried setting start_block directly in the indexer, and using execution plan with readonly tasks. Complains about missing blocks and exits. Formalising this to work as a config property is a necessary upgrade
Thanks