Add support to fides_consent cookie for root domains with second-level domains (co.uk, co.jp, etc.)

[NevilleS]

Bug Description

We currently automatically detect the root domain of the site by parsing the hostname and extracting the last two parts (e.g. "some.privacy.example.com" -> "example.com").

However, some websites will have a root domain with three parts, like "example.co.uk", so this existing automatic detection will fail and will attempt to set the cookie to "co.uk" instead!

Steps to Reproduce

n/a - this is easy to understand in the code, but actually hard to reproduce "in the wild" as we'd need to deploy to a website with this style of domain.

Expected behavior

We should either:

1. Automatically detect these types of "known" multi-level root domains
2. Provide a configuration option to override what the cookie domain should be

I'm partial to option 2 as it feels like a safer choice and gives the user control over this behaviour.

[NevilleS]

Note that some googling led me to https://github.com/peerigon/parse-domain, which confirmed that automatically parsing out the "effective TLD" is full of edge cases...!

[rsilvery]

@allisonking or @NevilleS do we still need to handle this?