ConditionalDefaultsLookup: allow to dynamically add conditions for evaluation

Why:
To facilitate the evaluation of conditions not directly
"known" by the lookup, eg: owned by extensions

What:

• Add ConditionalDefaultOptionsAddCondition hook which

runs before instantiating ConditionalDefaultsLookup allowing
to add conditions for evaluation in the $extraConditions
array.

• Evaluate the configured conditional default against the extra added conditions after evaluation of "known"

conditions.

Bug: T376918
Change-Id: Ife6f96397eafd61fdb40528aac315ddde1ef2774