[blazar] Third-party resource type plugins

Hi all,

I’ve just submitted a spec for making resources in Blazar follow a more explicit plugin architecture: https://review.opendev.org/c/openstack/blazar-specs/+/809485

The intent is to allow out-of-tree resource types, to allow deployers/operators to define their own abstractions. This could support some pretty wide-ranging implementations, like reserving bandwidth allocations on switches or perhaps access to other controlled/limited resources.

I hope that this change will also enable Blazar to be adopted by a wider set of users and use cases.

Please, have a look—it is currently proposed under Xena because there is not yet a Yoga spec section in blazar-specs.

Cheers, /Jason