Setting Up New Repo, Adding Files, etc.

[nv-rliu]

Closes https://github.com/rapidsai/graph_dl/issues/620
Closes https://github.com/rapidsai/graph_dl/issues/621

This PR updates a handful of files for the new nx-cugraph repository.

Proposed Changes

• Setup the CODEOWNERS file with proper roles each of the sub-directories.
  • Unblocked: https://github.com/rapidsai/ops/issues/3545 has created the new roles.
• Adding 5 "Issue Template" files, borrowing a lot of formatting/conventions from those inside the cugraph repo.
• Create new-issues-to-triage-projects.yaml
• Update pre-commit.yaml
• Add a ci/check_style.sh script to be used in CI
• Minor comments, adding lines to end of files, update copyright statement.
• Move the contents of the python/nx_cugraph/ directory up one level.

Note for Reviewers

• Need to ensure that the roles in CODEOWNERS are delegated properly. There is still a Warning that the file contains errors, and perhaps it's because the mentioned roles are "unknown", aka, need to be created for the rapidsai organization?
• I tested build.sh and its various CLI args to make sure it is working properly, but there might be additional code in there that can be safely removed.
  • Are lines 119-128 in build.sh are necessary for a pure-Python project like nx-cugraph? Can they be safely removed?
• You may notice a lot of "File was renamed..." changes. Those were mainly migrating files from python/nx-cugraph/ up two levels so nx_cugraph and _nx_cugraph all inside the root directory.

[rlratzel]

Do you think we need a python subdir at all? Maybe we can just have nx_cugraph at the root level, similar to what NetworkX and other pure-python projects do?

[eriknw]

🚀

[bdice]

Two small suggestions, otherwise the changes since my last review look good.