NIFI-13868: add pg-delete command to Nifi Toolkit

[grishick]

Summary

NIFI-13868

Adding pg-delete command to Nifi Toolkit. The command works the same way as deleting a process group via UI. If there are messages in PG queue, deletion will fail. I ported this change from Anetac's Nifi fork where I made it a while ago. We have been using this feature in production at Anetac for months now.

The code change to main branch is smaller than the one to support/nifi-1.x branch, because @markap14 has already added some of the functionality under NIFI-12898

Related PR for support/nifi-1.x branch: https://github.com/apache/nifi/pull/9387

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