Support hosting shortened URLs

[TimoGlastra]

Support the hosting part of shortened urls as described in the url shortening section of the OOB spec: https://github.com/hyperledger/aries-rfcs/blob/main/features/0434-outofband/README.md#url-shortening

I think this should be done after the work on the Out-of-Band record has been merged. We can then add an endpoint to the HTTPInboundTransport that when retrieved looks for an Out-of-Band record with an unique id (either the record id itself, or another id which allows to match a shortened url to an OOB record). We then return the OOB invitation stored in the OOB record.

The invitation shouldn't be allowed to be fetched indefinitely. So we either set a timeout, or do a check on the record state (or both).

This issue is only for hosting shortened urls, for retrieving see the relevant issue: https://github.com/hyperledger/aries-framework-javascript/issues/501

[TimoGlastra]

@jakubkoci what do you think of this approach? I think this fits quite nicely with the OOB record as it allows to easily store the invitation and allow it to be retrieved using an unique identifier. We've run into issues with non-shortened URLs for connectionless proof requests that are too large to scan. And even though we can solve it outside of AFJ, I think it would be nice to build an (optional) method into AFJ