Add Encoding & File to YAML template

[ajwans]

Many of the options to yab can be specified in a YAML template. In my case I want to specify a file to read the request data from and also to specify how the request is encoded.

This diff enables these options within the template file.

[CLAassistant]

All committers have signed the CLA.

[Dogild]

Thanks for the contribution, is there any chance to update the summary of the PR to get more context on this please?

[ajwans]

I updated the top comment, is that what you need?