Add wait for packet to be relayed function to e2e tests

[colin-axner]

Summary

While writing the e2e tests for ics20, I noticed the relayer did not relay my packets before the next assertion came. This issue was solved by adding a .waitForBlocks call. Several blocks were required to be waited on. Instead of waiting for enough blocks to be committed for the relayer to relay the packet, we should wait on the packet to be relayed by. I guess this can be done by waiting for a block to be committed and then querying to see if the packet was relayed, otherwise wait for the next block. Any other ideas?

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[chatton]

I think we could generalize this one step further and simply have a WaitForCondition(func() (bool, error)). This should be quite flexible and let us wait for arbitrary conditions to be met. We would also need to specify a timeout and some sort of polling interval.