add synctest with plan.update()

[barnabasbusa]

kt run . --enclave A --args-file pre.yaml

participants:
  - el_client_type: geth
    cl_client_type: prysm
    count: 2

kt run . --enclave A --args-file post.yaml

participants:
  - el_client_type: geth
    cl_client_type: prysm  
    count: 2
 - el_client_type: geth
    cl_client_type: lighthouse
    count: 4
    validator_count: 0 ?

kt enclave A should be updated with additional nodes.
Think about how validators are managed.

[barnabasbusa]

updating an image would also be very useful.