Refactor multiple client setup and clean up surrounding code

[JoshuaKrstic]

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• Updated where verifier clients are managed to be flexible to adding new verifiers in the future
• Cleaned up some surrounding code (like changing the token refreshing to only happen within a loop)
• Removed "ConnID" from the challenge as it seems to be unused.
• Updated the GCA rest client to lazily initialize its location to prevent requests from hitting the GCA when the workload doesn't use it as its verifier