Use plain text button in Duo batch update settings

What does this MR do and why?

Use plain text Apply to all button instead of the current Duplicate icon button

Why?

• We're going to use the existing Duplicate icon as the new Copy to clipboard icon --> Update icon - `Copy to clipboard` and deprecate... (gitlab-svgs#451 - closed)
• Duplicate as an icon will be deprecated
• This is the only instance we have of the Duplicate icon and it seems a text button would work just as well here

Screenshots or screen recordings

Before	After

How to set up and validate locally

Links

• ✂️ UX Paper Cuts 18.3 → Plan (#513105 - closed)