Add Indexed Merkle Tree info to the da layer

[MartinOndejka]

DA node needs to sign tuple of (ledger_hash, account_set_hash) and make sure both trees are reconstructible. Circuit allows to add entries to account set at any index, therefore sharing only changed accounts in ledger isn't enough.

There are 2 solutions:

1. Do the same with the IMT as with the ledger. Share the list of changed entries, openings to them, make sure the previous IMT is already reconstructible, apply changes to the openings and calculate the root hash.
2. Allow only appending entries from left by ensuring that the indices of new entries are the same (or +2 in case first 2 entries are low and high) as the indices in the ledger. Share openings to them and calculate the root hash.

[linear]

ZK-210 Add Indexed Merkle Tree info to the da layer

[L-as]

FWIW I will probably still restrict the tree to be filled in in order.