[FSSDK-9780] Return Latest Experiment When Duplicate Keys in Config

[Mat001]

Summary

• As a developer, I want to avoid non-deterministic return values in optimizely_get_config method so that I can anticipate the return values in my application logic.
• The problem: we have flag 1 and flag 2. We have experiment rule A with id 123 and experiment rule A with id 456 (same rule key). Flag 1 has the first experiment rule A, flag 2 has the second experiment rule A. Has a rule with the same experiment key.
  We want to avoid that, so we provide a check and a warning log.

Test plan

• write unit tests

Issues

• https://jira.sso.episerver.net/browse/FSSDK-9780

[jaeopt]

LGTM

[andrewleap-optimizely]

LGTM