Integrate Kate commitment into the L1

This MR aims to introduce the Kate commitment for a slot header. To do so we do the following:

1. We move the library lib_crypto/dal into lib_crypto_dal. This allows to introduce a dependency for lib_crypto_dal to lib_crypto. This is required to reuse helpers defining base58 encodings for commitments
2. We change a bit the interface of lib_crypto_dal to make it fit better with what is exposed. In particular, we implement properly the base58 encoding and remove the code from the dal_node.
3. We export the dal into the environment
4. We replace the current type of a slot header by the Dal.commitment datatype and adapt the tests accordingly

Notice that the next task for this MR is finish the semantics of the dal_publish_slot_header operation to check that a commitment is valid with respect to the defined slot_size. This is a bit more involved and will be implemented in a follow-up MR.