NIFI-6905 Prevent non-primary nodes to connect Twitter API when runni…

[k0urge]

…ng in primary node only mode.

Description of PR

GetTwitter processor, configured to run on primary node only, initializes connection to Twitter API from every NiFi cluster node, even on non-primary nodes.
Prevent non-primary nodes to connect Twitter API when running in primary node only mode. This Fixes bug NIFI-6905:

I updated the GetTwitter processor onScheduled() method to only create a clientBuilder without connecting it to the Twitter API.
Connection is now initialized by the onTrigger() method when it needs it (in primary node only mode onTrigger() never run on non primary nodes....).
Added onPrimaryNodeChange() to close connection on PRIMARY_NODE_REVOKED events.

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[markap14]

Thanks @kourge-ch ! Was able to verify that everything is working as expected and code review looks good. Thanks for fixing that! +1 merged to master.