Add p-media-container class

[petesfrench]

Done

• Add p-media-container class which adds .5rem of spacing above media elements

Fixes #4791

QA

• Open demo
• See that the image in the 'Media element with spacing' section is wrapped in a container that adds 0.5rem spacing to the top
• Check the wording of the documentation

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.

Screenshots

[webteam-app]

Demo starting at https://vanilla-framework-5012.demos.haus

[bartaz]

As we are adding new feature here, that's the point when we should bump the version to 4.9.0 in package.json, but also we need to add 4.9.0 section to releases.yaml, listing the change and linking to updated docs page.

[bartaz]

@petesfrench I guess you may need to rebase this branch on main to resolve conflicts.

[bartaz]

Sorry, forgot about this one. LGTM, thanks!