NIFI-6968 Create Connection Model Allows Multiple Adds

[nagasivanath]

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Description of PR

fixes bug NIFI-6968 Create Connection Model Allows Multiple Adds

Root Cause: In the process of creation of connection, the add / apply button is not disabled , due to which, when the network is slow & when the button is clicked twice unknowingly, the requests are sent multiple times , so multiple connections are created.

Fix: Disable the buttons when the add/update connection is in progress, enable them back after the action.

Impacted Areas: the same issue in case of configuring connections & clicking on Update, also the cancel button should also be disabled when the creation or modification is in process

Tested in : Add Connection, Update connection scenarios using the chrome's network throttling feature making the network very slow

After Fix: the screenshots are taken during the progress, so they are disabled
Update Connection -

Add Connection -

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