Dynamic payloads in variable

[GeorginaReeder]

Please describe your feature request:

In my opinion it would be very nice to have the ability to pass payloads into variables like this:

-var requesturl="/users/{{id}}"

where id is defined in the template like this:

path:
  - "{{BaseURL}}{{requesturl}}

payloads:
  id: payloads/id.txt

Describe the use case of this feature:

This feature would allow for more flexibility in executing injection attacks on multiple or changing request urls while keeping the same payload input

Originally posted by @TimMaasGeesteranus in #5755