Openbrokerapi

- Provide an option to provide a custom authentication implementing `openbrokerapi.auth.Authenticator`

- Pass error messages of `ErrBadRequest` to inform the platform about the issue details

- Fix [issue 211](https://github.com/eruvanos/openbrokerapi/issues/211) use keyword arguments to call broker functions from api

- ErrConcurrentInstanceAccess exception on an instance update, an instance deprovision, a binding or unbinding must return 422 not 500.
- ErrPlanChangeNotSupported exception must return 400 not 500.
- last_operation and last_binding_operation forward service and plan identifiers when provided

- Update dependencies
- Drop Python 3.6 support
- Migrate to Poetry

- Drop Python 3.5 support
- Fix ´bind´ in multi broker setup (117); thx vaxvms
- Removing requirement to have a space_guid and an organization_guid (116); thx rajahaidar
- Improve documentation; thx vaxvms
- Fix collections.abc deprecation; thx tammersaleh

- Introduce new error to return BadRequest
- Add **kwargs to catalog classes