Relax conditionally forbidden nature of prior_notice_start_day in booking_rules.txt

### Describe the problem

Presently, the spec prohibits specifying `prior_notice_start_day` in `booking_rules.txt` if `booking_type = 0` (Real time booking). However, some microtransit services exist that allow a rider to schedule a ride multiple days in advance if they choose in addition to being available in real time. I'd like to explore the possibility of relaxing the conditionally forbidden aspect of `prior_notice_start_day`.

### Use cases

C-TRAN's The Current microtransit service allows riders to schedule a ride up to two days in advance in addition to real-time:


https://mail.c-tran.com/thecurrent/current-faq

Here is a link to the main page for The Current service:
https://mail.c-tran.com/thecurrent

### Proposed solution

Remove "**Forbidden** for `booking_type=0`" from `booking_rules.prior_notice_start_day`

### Additional information

_Edited 6/17/25 to remove booking_rules.prior_notice_last_day from request_