update collection-index.yml for .NET Aspire feature

[danmoseley]

What type of PR is this?

• [X] Add a new dev container collection
• [ ] Update to an existing dev container collection
• [ ] Documentation/spec update
• [ ] Other containers.dev site update (UX, layout, etc)

Related Issues

• Related Issue #
• Closes #

Description

Adds the ".NET Aspire" dev container feature. Note- this name was previously used by another dev container feature coming from a different repo. That has been deleted from its repo two weeks ago so the name should be available for this one to take.

Collection checklist

If your PR contributes a new collection, please utilize this checklist:

• [X] Collection name
• [X] Maintainer name
• [X] Maintainer contact link (i.e. link to a GitHub repo, email)
• [X] Repository URL
• [X] OCI Reference
• [X] I acknowledge that this collection provides new functionality, distinct from the existing collections part of this index.