Etherlink/Node: Add chain_family
What
Introduces chain_family to the l2_chain type.
Why
For future heterogeneous l2 environment with different chain families coexisting in the same rollup.
How
The first commit introduces the type chain_family that currently supports EVM and Michelson.
The second commit adds this information to the Kernel configuration.
The third commit modifies the existing make_l2_chain_test to also test the chain family for the EVM case,
and adds a new test for the Michelson case.
Edited by Luciano Freitas