feat: add the pixi package manager to public index

[blooop]

What type of PR is this?

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

Description

This adds the pixi package manager as a devcontainer template

https://pixi.sh/latest/

Collection checklist

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

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

[Kaniska244]

Thank you for the PR. This can be merged.

With Regards,
Kaniska

[blooop]

I had a more in depth look, and I think this pr may not be correct after all. I gave it the name pixi because that is the only template I had added, but it won't be correct if I add more templates in the future. I have updates the index name to devcontainer templates by blooop match the format other repos are using.