enh(settings): removed background-gradient to ensure contrast ratio a11y requirements

[emoral435]

☑️ Resolves #42440

🖼️ Screenshots

🏚️ Before	🏡 After

Extra SS to check a random colors color contrast ratio

🚧 Summary

Removed the background gradient on the profile preview section of the settings to increase accessibility

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[emoral435]

/backport to stable28

[nimishavijay]

Nice! Looks good, additionally: we don't use #000000 for text, we only use #222222, so that should be the color of the text and the color that the contrast is checked against :)

[JuliaKirschenheuter]

Looks good!

Extra SS to check a random colors color contrast ratio

we don't need to pay attention on it, please test everything only on default background without changing color. We certificate only default background and everything else is not relevant for us ;)

[backportbot-nextcloud]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28

# Create the new backport branch
git checkout -b fix/foo-stable28

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts. Resolve them.
git cherry-pick abc123

# Push the cherry pick commit to the remote repository and open a pull request
git push origin fix/foo-stable28

Error: Unknown error

More info at https://docs.nextcloud.com/server/latest/developer_manual/getting_started/development_process.html#manual-backport