Public credential issuance with escrow account

[noandrea]

The user story is:

CredentialIssuer declares that

• it issues a credential
• for a price
• within a time limit

An applicant can send a transaction to request the issuance of a public credential

• the transaction must contain amount to cover the price of issuance

The amount is then locked in an escrow account.

When the Issuer issues the credential, the funds in the escrow account get transferred
to the credential issuer.

After the time-limit has expired, and if the credential has not been issued, then the
applicant can execute another transaction to cancel the credential request and
recover the funds from the escrow account.

[github-actions]

This issue was marked as stale because there was no activity for 15 days