[GENESIS] Make camino part of genesis fully optional

[evlekht]

Why this should be merged

In genesis json we have camino field which contains camino-specific data. Initial idea was that we'll keep all avax logic and introduce our own in addition to that, so both camino and avax tests can work with existing code. But there are still still some inconsistency in that.

If we'll try to run node with custom genesis json, which doesn't have camino field at all, like normal avax genesis, genesis parsing will fail cause of invalid initial admin address. This PR solves it by making whole camino field logic optional.

How this works

Make camino field pointer, so default value will be nil. Check for not nil before doing something with this field.

How this was tested

Existing unit-tests and e2e tests.
Manual start of local node with custom genesis without camino field.