Store that DMARC record is on org domain

[baknu]

DMARC record of organizational domain is effective for subdomain when the latter does not have its own DMARC record. Internet.nl already tests this way. However currently it is not stored in the database that the effective DMARC record was on the organizational domain. If we would store this info, we can 1) prevent incorrect conclusions wrt non-sending mail domains in the API and 2) display this info in the tech details on the website.

[gthess]

I believe that this is already implemented. We now have a "found on" field for the DMARC existence test.
@baknu could you verify and close?

[baknu]

Yes this is done and works in the Internet.nl frontend: #249 (comment)

However the info still needs to be included into the API output: #489