Enhance ConstraintOperator capability

[tkobayas]

…ares incompatible types

This PR is to enhance ConstraintOperator to be able to use alpha/beta index.

[tkobayas]

@mariofusco This PR is not a clear separation as you mentioned in kiegroup/drools-ansible-rulebook-integration#112 (comment)

This PR enhances ConstraintOperator to contain Index.ConstraintType, so a custom ConstraintOperator can have its own predicate while make use of alpha index. (I haven't implemented for beta index yet. I can do it later in this PR). Bare Index.ConstraintType can be both an operator and an index type. I leave it so that I can minimize the change. If you want further separation, feel free to let me know.

[tkobayas]

Updated with beta index support and unit test

[tkobayas]

If alpha index is effective, the predicate in the CustomConstraintOperator is not executed.

[tkobayas]

If beta index is effective, the predicate in the CustomConstraintOperator is not executed.

[tkobayas]

As commented above, if alpha/beta index is effective, the predicate in the CustomConstraintOperator is not executed. So implementing type check and error logging in the predicate doesn't work.

I guess alpha index is a more possible use case.

For example,

A user mistakenly wrote wrong rules like this.

condition: event.meta.headers == "AAA"

condition: event.meta.headers == "BBB"

condition: event.meta.headers == "CCC"

Then, an incoming event has meta.headers as a Map.

We can do type check in a predicate in a custom ConstraintOperator, but in the alpha index hashing case, the predicate is not executed and simply no rule would be fired. The user has no clue what is wrong in the rules.

If we want to rescue the situation, we need to implement type check at CompositeObjectSinkAdapter.propagateAssertObject, WDYT? @mariofusco