[REQUEST] Add auth type when account login is required

[emmambd]

What problem is your feature request trying to solve?
There are cases (like https://otd.delhi.gov.in/data/static/) where there is no formal authentication process for a GTFS feed (like registering for an API account), but there's no way to retrieve the feed without individually consenting to the Terms and Conditions.

Describe the solution you'd like
An auth type=4 for cases when an account has to be logged into or a UI element has to be selected to download the feed. Ideally we'd programmatically do this each time we want to download the feed.
Update schema in the README
Update python operations
Update API schema
Updating tests
(if downloading is not possible) Update batch processing to omit dataset storing for auth_type=4
Database changes for enum

Additional context
Example Feeds that Need a Login to Be Used:

https://opendata.transport.nsw.gov.au/dataset/a5ecd906-ce73-484c-8cea-fa6fecfe368e/resource/e25092cc-67a1-469c-b57a-20793c259486/download/ondemand_gtfsflex.zip
https://otd.delhi.gov.in/data/static
https://transitdata.io/city/1
https://transitdata.io/city/12
https://data.mobilitaetsverbuende.at/en/data-sets