Handle ELTS configuration

[noqcks]

What would you like to be added:

Right now xeol only handles EOL dates for standard support on products, but some products like Red Hat may have extended support dates. (In fact, Red Hat has multiple levels of extended support).

There should be some way to specify that a product has ELTS.

Why is this needed:

If this isn't implemented, organizations with ELTS on products will have inaccurate results.