Add dismissable perma tools info

[tinykite]

What this does

• Adds dismissible information about the Perma Browser Tools.
• Adds a css utility class, following the spacing tokens scale previously defined in the CAP static project.

Screenshots

Paragraph is visible by default, unless a user has previously clicked the close icon.

The position of the message shifts slightly for individual users:

The visibility of the content depends on the "perma_tools_reminder" key, which follows the naming pattern of the local storage object, "perma_selection"

Notes

• We were previously relying on a cookie to determine if this text is visible. Because this is a user preference that is exclusively used client-side in the browser, and doesn't need to be included in API requests, it felt like it might make more sense to include it in local storage, which we were also already using for other client-side UI preferences.
• There was some overlap between the legacy "Create a New Perma Link" header and the dismissible content that was preventing pointer events from being recognized on the close button. The easiest way to avoid this without introducing unnecessary changes to the legacy application seemed to be to introduce a utility CSS class, that we could easily add and remove if needed.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 70.11%. Comparing base (183aff7) to head (fc69dde). Report is 25 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #3515 +/- ## ======================================== Coverage 70.11% 70.11% ======================================== Files 48 48 Lines 6642 6642 ======================================== Hits 4657 4657 Misses 1985 1985 ```

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[tinykite]

Only thing is that means all users will have this preference unset when we switch over. If we're indeed okay with that: we should probably make sure that the linked "browser tools" page is up to date and is ready for a bunch of fresh views. Something to bring up with the product team, methinks.

That's a reasonable ask — I'll touch base with Clare.