Feature Request - accept and record a "note" (max 64 chars) with /register endpoint

[jvanasco]

It would be useful if a user could pass a generic message (max 64 ascii chars) to the /register endpoint, which is then saved to the records table alongside the newly generated account.

The use-case: I would like to pass in an identifier (FQDN, application id, test-information, etc) when generating an acme-dns account on /register, to help identify records solely within the acme-dns database. This would greatly simplify audits of the acme-dns database to identify stale data that can be safely removed (an old LastUpdate might be for a domain that is still enrolled in the system, but currently using http-01). This would also make it easier to handle testing against a staging server, and make some local testing easier as well.