Investigate ways to allow users to provide options

[JoshuaKGoldberg]

Auto-detection of frameworks is nifty and all, but:

• It's only a matter of time before folks will want to specify their own libraries
• Some libraries are proving rather difficult to auto-detect (e.g. Find a way to detect whether Mocha is the active test framework #10)

What things will users want to provide as an option?

• Test framework?
• Spy library?

How should they be able to provide these options?

[JoshuaKGoldberg]

For now, let's just have a request/settings object be passed to cft with those two fields.