NIFI-8062: make tabs functional with keyboard

[sardell]

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Please provide a short description of the PR here:

This PR adds keyboard functionality to the custom tabbs jquery plugin.

Testing

Build NiFi locally, open the UI and locate anywhere that uses tabs (for example, inside the Global Menu's Summary window). Click on a tab. Navigate to the next tab by pressing the Tab key. Navigate back to the previous tab with Shift + Tab. Select a tab by focusing on it and pressing Enter or Space. You'll notice focus styles have been added.

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[markap14]

Verified that I'm able to switch between tabs in the processor config dialog and in the Controller Settings dialog. Based on the code changes, I think this should apply to all dialogs. Of note, in order to verify that, I had to click on one of the text boxes / inputs within the form and then press shift-tab to get to the tabs. Otherwise, just pressing tab jumped all over the place, as it selected elements in the background (like the search box) even though there was a dialog open. We should probably only allow tab to jump to elements in the dialog when a dialog is present. That said, I don't think it needs to be done in this PR/Jira. So I'm a +1. Will merge to main. Thanks @sardell !