[Google Flights API] Support "Separate & self-transfer tickets" filter

[NateSkiles]

A customer requested we support the "Separate & self-transfer tickets" filter from Google Flights:

Description:

It may be cheaper to buy flights as separate or self-transfer tickets from one or more partners. Depending on the partner, separate and self-transfer tickets may be booked separately, or together. Learn more

This filter has two options:

• Show separate & self-transfer tickets (Default)
• Hide separate & self-transfer tickets

This filter essentially hides all options that split the trip between two different airlines:

Google Flights

Intercom

[oceansize]

Another customer requested this:

Intercom