WATCHPUG - Slippage tolerance for Synapse should not be specified as constant values of `0.95`, `0.91` about 2022-10-mover-judging

[McMannaman]

#103
is more duplicate of
#53

this issue has no duplicates as far as I saw through the issues.

This is a good deep dive into the interaction btwn TopupProxy and particular bridge ABI.
Yes this is a compromise. As we work with stablecoins and always set the in/out token
as USDC (or its equivalent) these values serve as a kind of sanity checks and we expected the
actual slippage to be much tighter. So if these thresholds are not met, bridging would not
happen which suits us (the slippage is way off and we may consider switching to another bridge or
otherwise somehow investigate the situation.

But we don't want to set it too tight to get things reverted, or complicate the flow for the user to
manage slippage or deal with reverted txs because of slippage. If the slippage is high for stablecoins,
we consider another bridge provider. Hope this explains our point.

We very much appreciate the effort done to underpin this with a precise particularity.