Modify github-access engine to offer flexible access to other OAuth2 data sources #71
Description
Currently this engine only supports GitHub but it can support everything passport.js library supports through simple configuration (that is instead of hard-coding configuration for github we can leverage module installation pattern (we use in ESLint engine) and no-boilerplate-passport to provide configurable access to any other OAuth2 data source.
Furthermore remove multi-tenancy which is just confusing as lazy is not multi-tenant and it's not even being (correctly) used.
Finally rename github-access engine to oauth2-access.