temporaryConfigDirectory: no package.json file needed for Tests.

[gagoar]

This PR provides a helper to create on the fly a package.json file with the desired options.

_this is the solution we discussed on https://github.com/cjoudrey/graphql-schema-linter/pull/196#discussion_r352382723_

• caveats: given that we do create a pacakge.json per every run, this will affect the speed of the suit. altho is not noticible now.
• benefits: the paths to customPaths and customRulePathss are always absolute from the developer stand point, but this is solved by the helper providing the relative path to the location of the tempDirectory created. it also prevent us from having issues when 2+ tests need the same package.json like we saw in https://github.com/cjoudrey/graphql-schema-linter/pull/196

This solution could also be applied to rc_file and js_file respectively

I have the same solution with sinon. I can share it as well.

[gagoar]

after this PR is merged, I can work in make it generic to use it in the other config cases.

[cjoudrey]

Thanks again! 😄