When I converted Manifester to pyproject.toml, I did not include a
`project.scripts` section. As a result, an executable for the Manifester
CLI is not installed when the Manifester package is installed. This PR
adds a `project.scripts` section to pyproject.toml so the Manifester CLI
is easily accessible.

  Command-line interface for manifester.

Options:
  --help  Show this message and exit.

Commands:
  delete        Delete subscription allocations in inventory and...
  get-manifest  Return a subscription manifester based on the settings...
  inventory     Display the local inventory file's contents. to codeql-analysis GitHub action