Implement changes in fullsync to support warpsync

[dimartiro]

When we execute warp sync we need to

1. Retrieve the last finalized block following auth changes and verifying justifications
2. Retrieve that block state
3. Continue the sync from that latest block

We have 1 solved with #3183 and 2 solved with #4238 but we need to solve the 3rd point by modifying the full sync to allow it to start from a specific block.

In order to do this, we are going to modify the configuration when we create the full sync strategy to let it know from what block to start.