Revert "Remove tests of chaincoin default rate provider (#2189)"
Revert "Remove tests of chaincoin default rate provider (#2189)"

This reverts commit 56daf347b914cf60a99128b96fdca94072af95a5.

btcpayserver/btcpayserver,btcpayserver/btcpayserver,btcpayserver/btcpayserver,btcpayserver/btcpayserver