Tezt-cloud: run accuser

Run an accuser together with a DAL node when the new CLI arg --accuser-slot-indices is given.

On top of !16186 (closed).

Testing

Run something like: dune exec tezt/tests/cloud/main.exe -- dal --localhost --stake 1 --accuser-slot-indices 2 -v

You should see the accuser running, eg:

[accuser-0] Jan 12 05:20:23.074: block BLAtEa9GxzDfodPc1FBwpst7Fd62EeHAkAhBNidMNjzYZLuZD45 registered