Blacklist address endpoint

[j-mueller]

Add an endpoint that allows us to blacklist an address.
Inputs: The address to be blacklisted.
Fails if the submitter is not the issuer of the stablecoin, or if the address is already on the list.

• Offchain endpoint like the ones in Wst.Offchain.Endpoints.Deployment
• Test case for happy path in Wst.Test.UnitTest
• API route (POST) in Wst.Server.Types.BuildTxAPI
• Handler for the route in Wst.Server