"dev/linter.sh": add python compatible command for "isort" and "black"

https://github.com/facebookresearch/detectron2/blob/b03bbd7df056340c69fb4164c90088cf00835e2d/dev/linter.sh#L21-L23

https://github.com/facebookresearch/detectron2/blob/b03bbd7df056340c69fb4164c90088cf00835e2d/dev/linter.sh#L24-L25

We can add an if-else statement in the above code-blocks to run `isort` and `black` with python as `python -m isort -y -sp . --atomic ` and `python -m black -l 100 .` respectively. This is the same as done with `flake8` (shown below).

https://github.com/facebookresearch/detectron2/blob/b03bbd7df056340c69fb4164c90088cf00835e2d/dev/linter.sh#L27-L32

If this change is valid, I would open a PR for that. Thanks!

Open dev/linter.sh and inspect the isort and black command blocks at the linked lines, comparing them with the flake8 block below. Verify the Python module forms for both tools and confirm that the linter script runs them successfully; done means Python-compatible commands are available for isort and black.

Written by the indexing model from the issue text.