Implement GET & DELETE APIs for Veraison Provisioning Interface!

Current Interface to Veraison Provisioning only allows Submitting Endorsements (Reference Values and Trust Anchors)!

However one should be able to Fetch these endorsements, to check, whether the submissions are as per the expectations
as well as to query what all has been submitted so far!

In addition to this an Endorser should be able to DELETE the Endorsements, once submitted.

This issue tracks this enhancements to introduce GET & DELETE APIs.

Please note: This issue was to be migrated from Veraison/veraison repository where originally it was created,
but got lost in transit!