PyDrive2 as a protocol for fsspec

Hi!

I created a sample file on my Google Drive `hello.txt` and made it accessible for `Anyone with the link`: https://drive.google.com/file/d/1I_bokg0Fejy7dVxNkZcJD4gCagawLIVY/view?usp=drive_link

E.g. I have an `fsspec`-using program `catfsspec.py`:
```python
import sys, fsspec
with fsspec.open(sys.argv[1], 'rt') as f:
print(f.read())

# python catfsspec.py file://hi.txt
# planet
```

Does installation of PyDrive2 auto-register a protocol with fsspec automatically (like sshfs does: https://pypi.org/project/sshfs/ )? Is it possible to access my sample Google Drive file

Ideally, I think being able to do the following would make a lot of sense:
```shell
# should not be needed for accessing anon-acessible files: export FSSPEC_GDRIVE_SECRET_TOKEN=$(python -m pydrive2 auth)
# or maybe export FSSPEC_GRDRIVE_CLIENT_JSON=client_secrets.json

python catfsspec.py pydrive2://1I_bokg0Fejy7dVxNkZcJD4gCagawLIVY
# world
```

Start with the proposed `python -m pydrive2 auth` entry point and fsspec's protocol-registration requirements. Check how anonymous access to the linked Drive file and authenticated access would map to the proposed environment variables and `pydrive2://` URI. Done means documenting or implementing a clear supported access path, including authentication behavior.

索引モデルが issue の本文から書いたものです。