Webui Add Custom Form to Auth Page

[andrewbaldwin44]

Proposal

1. Allow the auth form to be configured with any inputs. The configuration for the inputs use the same API and the same component as the locust custom arguments
2. Added an example of the auth custom form and updated the docs
3. Add tests for the custom inputs, the password input, and the numeric input
4. Custom arguments isSecret field will now have a visibility toggle in the webui

Screenshots