Feature: Add support for downloading a single repo, branch, or workflow

[sadreck]

Splitting #187 into multiple PRs as requested.

• Added the option to download a specific repo, using --repo-name "CycodeLabs/raven".
• Added the option to download from a specific branch, using --repo-name "CycodeLabs/raven@v1.0.6".
• Added the option to download a specific workflow file, using --repo-name "CycodeLabs/raven" --workflow "test_pr.yml".
• Both single repo and specific workflow arguments can be set multiple times, just like with the account-name.
• Added some validation checks when scanning invalid/non-workflow files that end up being in the ./workflows directory of a repo.
• Added integration tests for all of the above.

New feature command line usage:

Download a single repo - default branch

python3 main.py download repo --token "$GITHUB_TOKEN" --debug --clean-redis --repo-name "nextcloud/server"

Download a single repo - specific branch

python3 main.py download repo --token "$GITHUB_TOKEN" --debug --clean-redis --repo-name "nextcloud/server@fix-dav-properties-column-type"

Download specific workflow from repo

python3 main.py download repo --token "$GITHUB_TOKEN" --debug --clean-redis --repo-name "nextcloud/server" --workflow "cypress.yml"

Run Integration Tests

pytest -v tests/integration/