Replace ajax methods in select2 instances

What does this MR do?

Replaces uses of jQuery.ajax within our select2 usage as part of our transition to jquery-slim which will remove the ajax functionality.

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
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Security

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part of #321859 (closed)