Picked commits from latest release to resolve issues in 2.3.x

[rashidsp]

Summary

Picked following commits from 3.0 to resolve issues in 2.3.x

• Decision service: Return null variation if experiment key does not exist in feature's experimentIds array.(fix(decision_service): Return null variation if experiment key does not exist in feature's experimentIds array. #206)
• Decision service: Added bucketing id in getVariationForRollout method (fix(decision-service): Adds bucketing id in getVariationForRollout method. #200).
• Event tags: Do not exclude falsy revenue and event values in the event payload. (fix(event-tags): do not exclude falsy revenue and event values in the event payload #213)

[mikeproeng37]

@rashidsp can you include the bullet points in the summary as unreleased items in the README.MD for this release branch?