Allow specifying the topology used for Hermes tests

[ljoss17]

Proposal

The current state of Hermes, e4be3e0, creates fully connected chains when running tests with more than 2 chains.

This impacts the run time of some tests, for example tests::forward::forward_hop_transfer::test_ibc_forward_hop_transfer can take up to 682.193 seconds to pass. Most of the time is spent in the connection and channel handshake as the bootstrap is fully connecting the 4 chains.
This is not necessary, if the chains are connected linearly, A -> B -> C -> D, the test would still work.

It should be possible to specify the topology used for nary chain tests in order to reduce the run time of some tests.

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