Address Issue #258: Configuration predicate to control dependency graph creation

[mcumings]

Adds a new configuration option to allow the consumer to provision of a Predicate<Configuration> instance to customize what Configuration instances should be considered when building the dependency graph.

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For your consideration, adding something like this would be very helpful for us. Appreciate the work y'all have done thus far.

Note that the choice of Property<Predicate<Configuration>> was used because:

• Use of gradle properties allows the value to be changed all the way up until execution, which gets around afterEvaluate issues
• It exposes the actual Configuration instead of just its name

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