Editor: Display notifications always on top

[tkohr]

Description

This PR raises z-index of div around notifications-container to make sure they are always displayed on top (including hovered buttons).

Commit related to the issue (that may be needed for other cases?) : 4ac94ad

Screenshots

Quality Assurance Checklist

• Commit history is devoid of any merge commits and readable to facilitate reviews
• If new logic ⚙️ is introduced: unit tests were added
• If new user stories 🤏 are introduced: E2E tests were added
• If new UI components 🕹️ are introduced: corresponding stories in Storybook were created
• If breaking changes 🪚 are introduced: add the breaking change label
• If bugs 🐞 are fixed: add the backport <release branch> label
• The documentation website 📚 has received the love it deserves

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[github-actions]

Affected libs: ``,
Affected apps: metadata-editor,

• 🚀 Build and deploy storybook and demo on GitHub Pages
• 📦 Build and push affected docker images

[coveralls]

coverage: 84.986% (+1.3%) from 83.736%
when pulling 00ae4a2 on me-notifications-on-top
into 48c95d3 on main.

[github-actions]

📷 Screenshots are here!

[jahow]

thanks :) the z-index of hovered/active buttons was raised to 10 so that buttons' outlines appear above others in that case, so we have to keep it I think

[tkohr]

Alright, thanks for the info @jahow !