mediator: use did-exchange instead of connection protocol #1151
Description
After merging significant updates of did-exchange in #1097, we are now ready to replace establishing didcomm connection in mediator from legacy connection #160 protocol https://github.com/hyperledger/aries-rfcs/blob/main/features/0160-connection-protocol/README.md to did-exchange https://github.com/hyperledger/aries-rfcs/blob/main/features/0023-did-exchange/README.md