[Form Analyzer] Add 'guest' to signup regex in analyser

[dbajpeyi]

Reviewer: @GioSensation
Asana: https://app.asana.com/0/1205996472158114/1208414891646031/f

Description

On jcrew.com, the guest checkout form is treated as a login one. This is because the Have an account? Sign in text seems to score it on the login side, however multiple attributes with guest or Guest in the string and attributes are ignored. Such checkout forms are used in plenty of shopping sites, so it's likely that guest should be scored rather as a signup.

Adding guest to signup regex should work. I am also adding it to conservative one, I think it's a pretty strong indicator for signup.

Steps to test

1. Go to Jcrew.com
2. Add a product to the bag, and click on checkout (from the dropdown)
3. In the bag, go to checkout and click on "Continue as guest"
4. Guest form should have email protection showing: