[DOCS] Import value lists: renamed button, new flyout UI

[joepeeples]

Description

The UI for importing value lists has changed in 8.4:

• The "Upload value lists" button on the Rules page has been renamed "Import value lists". Confirmed that this changed between 8.3 and 8.4.
• The UI has changed from a modal to a flyout. Functionality appears the same, but "upload" has been revised to "import" in UI copy.

Refer to comments at #2244 (review) for locations to update, and search for any references to the old button and UI names.

OLD:

NEW: