Add sidecar.app_name config variable

[wilsenhc]

This PR adds a new config variable sidecar.app_name.

Currently I'm working on a rewrite of an application which uses Sidecar, and for both apps the APP_NAME is exactly the same (since one will eventually replace the other one) and when deploying Sidecar functions which are named the same one replaces the other.

This could solve then problem, letting us define a different internal name when deploying to AWS

[wilsenhc]

Doesn't make sense to me why almost all prefer-lowest tests are failing.

Any thoughts on that? @aarondfrancis

[aarondfrancis]

Amazing PR, thank so much for adding the tests and docs as well. That's a huge help!

I adjusted the test just a little bit, and also made the prefers-lowest tests pass by mucking around with the getEnvironmentSetup thing. Apparently that's the old name for it, so it works with the lowest constraint. (See: https://packages.tools/testbench/basic/define-environment.html#define-environment.)

Thanks again! I'll cut a release with this soon 🎉

[wilsenhc]

Thanks for the help with the tests!

And I appreciate that you liked it 🥳

Hope to see the new release soon to upgrade the projects where I'm using the package.

Thanks Aaron!