Add CA and ADCS Template metadata to Pkcs12

[cdelafuente-r7]

This adds the following metadata to Pkcs12:

• CA: the certificate authority that issued the certificate.
• ADCS Template: the AD CS certificate template used to issue the certificate.

The data is now serialized in the Pkcs12's data field with the following format: msf_pkcs12:<base64 cert>:<ca>:<ADCS template>.

[adfoster-r7]

Thanks! I'll just swap this PR into draft mode until we've wired up the corresponding UI changes in Pro to support consuming this metadata

I'm thinking this particular approach would require additional migration logic to support going from the old format to the new format, otherwise folk that have existing pkcs12 certs in their database might run into problems - but we can cross that bridge once things are wired up into Pro

[cdelafuente-r7]

Yes, absolutely, I agree. Additional migration logic will be a good idea.

[cdelafuente-r7]

Closing this PR since the head branch is on rapid7 repo. I'll open a new PR with the correct head branch.