Make OIDC Layer more flexible in data store

[chmreid]

Implement changes mentioned in DataBiosphere/data-store#80

Making the OIDC layer more flexible involves several aspects:

• generalizing the security decorator on various API endpoints to work better with whatever OIDC provider we happen to be using
• making it easier to swap out which OIDC provider we're using, without having to do a bunch of copypasta of existing methods
• allowing us to save code for the existing Fusillade auth approach, but also swap it out with Auth0 for our short-term effort

Definition of Done: the code in dss/util/security.py has been broken out into several parts that are more modular:

• security decorator can take arbitrary args/kwargs and pass them to auth backend
• auth backend is object-oriented, one class per auth provider (Fusillade, Auth0, etc.)
• auth provider base class provides one public method, which must be implemented by every auth provider, and which is called by the security decorator, and which is passed arbitrary args/kwargs by the security decorator

This is underway and mostly done in #103 (merged)

Also done in #113 (merged)

[chmreid]

PR #103 is completed, but still more work to do

PR #112 and #113 will add additional flexibility for decorator arguments

[chmreid]

113 merged, this can be closed!