Add the ability to directly discrimate on name

[shawkins]

For operators that have multiple dependent resources of the same type a common pattern is for those to be discriminated by name. While ResourceIDMatcherDiscriminator can account for this it does so by iterating over the list of resources. For an operator managing a fleet of resources this will eventually introduce unnecessary overhead. Ideally a built-in mechanism should be able to distinguish by name.

Similarly IndexDiscriminator could be promoted out of the samples.