Adding Copyright, enforce license headers on all files

[pearce8]

Adding the top level copyright. Which of the files should have the copyright at the top?

• package.py that our team develops in Benchpark? What happens to copyright when we push to Spack builtins?
• application.py that our team develops in Benchpark? What happens to copyright when we push to Ramble builtins?
• system configs?

[pearce8]

@slabasan Can you please work through a PR to check the copyright in each file?

[scheibelp]

Overall this seems good: removing licenses in various files leads to a failure in the verifier (as desired), and modifying the license identifier also causes a failure (as desired). Constraints on date also appear to work (although error message isn't clear in that case)

1. (minor issue) if I change configs/ats4/variables.yaml like so:

-# Copyright 2023 Lawrence Livermore National Security, LLC and other
+# Copyright 2021 Lawrence Livermore National Security, LLC and other

then the error message is unclear IMO

/Users/scheibel1/Desktop/benchmarking/benchpark/configs/ats4/variables.yaml: SPDX license identifier missing
1 improperly licensed files
 files with wrong SPDX-License-Identifier:   0
 files not containing expected license:      1

2. (I assume this is fine) if I change configs/ats4/variables.yaml like so

-# SPDX-License-Identifier: Apache-2.0
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)

then I get a failure (which I assume is acceptable, even though mixing these licenses is fine, we don't want to give flexibility on that).