Scope and purpose

Follow up to #3458, and necessary to position popovers in #3531.

• This PR adds support for positioning the popover on multiple sides: left, top, right and bottom. The side is configured with the data-side attribute, as described in the styleguide.
• The styleguide has been updated with the new data-side attribute, and the example was updated to use a data-side="right" data-align="start" configuration.
• data-align="center" was removed, as it is not likely to be used, and to simplify the code for multiple sides.
• _popover.scss was refactored to be more readable and reduce unnecessary nesting. It should be easier to follow the logic now.

I'm a bit uncertain if putting the data-* attributes on the .popover container was the best idea (the styles become a bit convoluted). We might want to consider moving data-side, data-align and with-arrow to the .popover-content container instead. Alternatively, combine the attributes into data-position="bottom-start" etc. However, this requires refactoring a lot of files, and would cause conflicts with #3531.

Screenshots

	Start	End
Bottom
Left
Top
Right

Contributor Checklist

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• Added a changelog fragment for towncrier
• Added/amended tests for new/changed code
• Added/changed documentation
• Linted/formatted the code with ruff, easiest by using pre-commit
• The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• This pull request is based on the correct upstream branch: For a patch/bugfix affecting the latest stable version, it should be based on that version's branch (<major>.<minor>.x). For a new feature or other additions, it should be based on master.
• If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done
• If this results in changes in the UI: Added screenshots of the before and after
• If this adds a new Python source code file: Added the boilerplate header to that file