`pelicanplatform.org` is missing a DMARC record

[jhiemstrawisc]

A user reported to security@pelicanplatform.org that our domain is missing a DMARC record, which leaves us vulnerable to having emails spoofed from our domain.

We should create the needed record along with other typical/applicable email authN methods while we're at it (e.g. DKIM, SPF, etc.)

[jhiemstrawisc]

Pinging @brianhlin and @CannonLock

[brianhlin]

@CannonLock the Brian Council has decided to delegate this one to you. LMK if you have questions!