MINIFICPP-2462 - Divide libminifi

[adamdebreceni]

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[james94]

Is there a Jira ticket associated with this PR effort? This seems like a huge refactoring contribution.

[szaszm]

• rename /core to /minifi-api, /minifi-api/include is in the include path, e.g. #include "minifi-cpp/core/FlowFile.h"
• ProcessCpuUsageTracker, Cron shouldn't be in extension-utils

[adamdebreceni]

Closing this in favor of #1902