Add support for alternate vaos-service route

[devin-mccurdy]

Note: Delete the description statements, complete each step. None are optional, but can be justified as to why they cannot be completed as written. Provide known gaps to testing that may raise the risk of merging to production.

Summary

• This work is behind a feature toggle (flipper): YES
• This work is behind the va_online_scheduling_vaos_alternate_route feature toggle.

This adds support for the future ability to set an alternate route for vaos-service that can be used by the vaos module. The alternate route isn't defined yet, and vaos-alt is a placeholder, which is why the flag is off by default.

Related issue(s)

• https://app.zenhub.com/workspaces/appointments-oracle-health-integration-65a6e99ea522640e4d09393b/issues/gh/department-of-veterans-affairs/va.gov-team/93478

Testing done

• Future work that implements the alternate route will test functionality.

Screenshots

N/A

What areas of the site does it impact?

None

[drewconnelly]

LGTM