Add outofband credential-offer

[DaevMithran]

The out of band protocol doesn't support the attachment type credential-offer yet. I added my code in outofband receive_invitation to receive a credential offer and send a credential request.

The receive_offer and create_request functions worked perfectly , But I am facing a connection_record not found error while the issuer agent executes credential_request_handler script. I am including the logs below.

`

File "/home/indy/aries_cloudagent/core/dispatcher.py", line 198, in handle_message
await handler(context, responder)
File "/home/indy/aries_cloudagent/protocols/issue_credential/v1_0/handlers/credential_request_handler.py", line 39, in handle
context.message, context.connection_record.connection_id
File "/home/indy/aries_cloudagent/protocols/issue_credential/v1_0/manager.py", line 470, in receive_request
session, connection_id, message._thread_id
File "/home/indy/aries_cloudagent/protocols/issue_credential/v1_0/models/credential_exchange.py", line 206, in retrieve_by_connection_and_thread
{"connection_id": connection_id} if connection_id else None,
File "/home/indy/aries_cloudagent/messaging/models/base_record.py", line 250, in retrieve_by_tag_filter
cls.name, tag_filter, f", {post_filter}" if post_filter else ""
aries_cloudagent.storage.error.StorageNotFoundError: V10CredentialExchange record not found for {'thread_id': '56ccbd83-3800-41a8-907c-fcbedeebb706'}, {'connection_id': '737ca643-7f05-470a-8b47-89fafb11a83d'}

`