allow setting of gitlab scope from env or settings file

[karcaw]

This changes the default of SOCIAL_AUTH_GITLAB_SCOPE to the empty list, as well as allowing it to be set by the settings file or the env. Of note, the social login adds read_user to this list, which is enough for login, and as such the [] default should be proper in most cases.

This should fix #434
This Should fix #431

I also added a settings dumper that is useful for debugging, and shell scripts, which may help with #432

[vsoch]

Looking good! Last item of action - please bump the version in https://github.com/singularityhub/sregistry/blob/master/VERSION and add a note to the CHANGELOG. If you'll be making a few PRs, we will put them all under this new version.

[vsoch]

@karcaw for linting, you can install pre-commit locally (and use our requirements.dev.txt to do so) and fix the errors

sregistry/.github/workflows/main.yml

Lines 21 to 29 in ee23901

	- name: Setup black linter
	run: conda create --quiet --name black black
	- name: Lint and format Python code
	run: |
	export PATH="/usr/share/miniconda/bin:$PATH"
	source activate black
	pip install -r .github/dev-requirements.txt
	pre-commit run --all-files

[vsoch]

Nice job @karcaw !