Requirements Scan in multi-type project: prompt for which project files to scan

[kgartland-rstudio]

When you do a Requirements scan in a multi-type project, the requirements.txt file is populated with all packages across each project file. Instead, when multiple-projects are detected, can we prompt the user to select which project they'd like to scan against?

Bonus points: prompt the user to select the project file and name their requirements file and select the associated Configuration, then add the new requirements file to the Configuration pacakge-file filed.