HTTP Endpoint to retrieve issuer DID configured in the service

Closes #10 (closed)

@yordan.kinkov @valerii.kalashnikov

added DevInProgress Need review labels

requested review from @tziai

assigned to @lyuben.penkovski

LGTM

merged

mentioned in commit dfe8e2c0

@tziai I'm merging everything quickly, cause we're in a hurry to do demo tomorrow and there's still a lot of things to test and integrate. You can still look and comment if you see something for improvement.

mentioned in commit 179c20ee