Update Keplr config when a custom bech32 prefix is used in monogen

[natebeauregard]

Currently, the wallet integration server expects the bech32 prefix to be the default value ("cosmos"). However, a custom prefix can be used if the --address-prefix {prefix} flag is run with monogen.

We'll want to update the monogen script to modify the Keplr bech32 config as well with the expected prefix if a custom prefix is passed in through the monogen flag.