AO3-7359 Action to copy admin 2fa backup codes

[brianjaustin]

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Issue

https://otwarchive.atlassian.net/browse/AO3-7359

Purpose

Add a button (only visible if Javascript is enabled) to the admin two-step verification backup codes page:

Testing Instructions

To be added in Jira once the design is fully settled

Credit

Brian Austin (they/he)

[sarken]

My comments keep vanishing and reappearing, so hopefully they'll be here once I hit this button... 🤞

[sarken]

Since we're doing something rather than going somewhere, can you make this a button? It's better for accessibility and it spares us from having to set the href to # and disable the default link behavior.

[sarken]

Does defer work on inline JavaScript now? I thought it was just for external scripts and inline scripts still needed to be included at the end of the body (we should be able to do that with content_for :footer_js) to avoid blocking page rendering.

Also, minor nitpick, the quotes are missing on type="text/javascript"

[sarken]

We prefer titlecase for button text, so "Backup Codes Copied!" (which is admittedly a little odd with the exclamation point -- I'd suggest plain "Copied!" to avoid that, but that would cause a more drastic change in the button size) and "Copy Backup Codes to Clipboard".