Resolve "Some TAs get access denied when clicking "approve""

What does this mr do?

The following was observed (as documented in the issue):

"TAs double click the approve button, causing 2 network requests. As the preauthorization checks if the request hasn't already been approved, the second click gets an Access Denied error, after the first click correctly approves the request".

A fix was implemented, but a further "safety-net" was implemented by disabling the button after it was clicked.

Actions taken to fix bug

Add JS to check the validity of the fields, and disable the button if the field is valid and the respective button was clicked.

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made and the bug I fixed.
• A test was created to test the bug. ~ The absence of something like Selenium prevents this from being tested.
• I have updated the documentation accordingly.
• I adhere to the style guide.

Closes #105 (closed)