NIFI-6587 - Fix: Unable save sensitive property value that equals masked value

[rfellows]

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Description of PR

There was an issue where the Apply button on the Edit Parameter dialog wouldn't be enabled if the parameter value entered matches the masked value that the server sends to the UI (******** - 8 asterisks). This PR fixes that as well as ensures that Set Empty String checkbox is reset on dialog close like the other input fields.

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[scottyaslan]

Thanks @rfellows this has been merged to master.