Add slight gradient to "show more" block

[jahow]

Description

This PR improves the "show more" component (gn-ui-max-lines) visually by adding a gradient on top:

Also fixes a layout issue within the Datahub if the data producer has no logo.

Architectural changes

none

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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This work is sponsored by Swisstopo.

[github-actions]

Affected libs: ui-elements, feature-catalog, feature-record, feature-router, feature-search, feature-map, feature-dataviz, ui-catalog, ui-search,
Affected apps: metadata-editor, datahub, demo, webcomponents, map-viewer, search,

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

[coveralls]

coverage: 86.136% (-0.2%) from 86.337%
when pulling d64f956 on add-show-more-gradient
into 7639a97 on main.

[github-actions]

📷 Screenshots are here!

[ronitjadhav]

@jahow Tested the changes and everything works as expected.