NIFI-7459 change nifi-stateless to use NarClassLoader

[mark-weghorst]

Description of PR

Changes nifi-stateless runtime to use the NarClassLoader instead of URLClasssLoader, this resolves issues with the confluent schema registry controller not initializing in stateless

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[github-actions]

We're marking this PR as stale due to lack of updates in the past few months. If after another couple of weeks the stale label has not been removed this PR will be closed. This stale marker and eventual auto close does not indicate a judgement of the PR just lack of reviewer bandwidth and helps us keep the PR queue more manageable. If you would like this PR re-opened you can do so and a committer can remove the stale tag. Or you can open a new PR. Try to help review other PRs to increase PR review bandwidth which in turn helps yours.