Provide guidance for relayers as gas consumption for packet relay becomes arbitrary with ICA/ICQ

[AdityaSripal]

As applications expand beyond ICS20 into more dynamic use cases like ICA (and even interactions between ICS-20 and smart contracts), the gas spent to receive a packet/acknowledgment is no longer predictable.

Thus, relayers may have issues processing packets with the current gas choices.

This issue is to offer guidance for how relayers should handle this upcoming problem both in the immediate and long-term.

cc: @ethanfrey @womensrights

ref: #1660

[ethanfrey]

I agree.

As a note, I looked at the ref and was confused how you could get 100 issues/prs in only 16 days.