Enhance KieCDIExtension to allow optional injections

Description of problem:
Currently KieCDIExtension will inject kieSession, KieBase or KieContainer to mandatory injection points:

@Inject
@KSession
private KieSession ksession

although sometimes it might be worth to allow optional injections as well to be aligned with CDI in general:

@Inject
@KSession
private Instance<KieSession> ksession

This is one of the enhancement needed for WebSphere support as apparently there is a bug in CDI implementation used by WebShpere that does not provide injection points when CDI extension is used for managed beans - POJO. This is still under evaluation but wanted to explain why it is required.

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