Add devcontainer-config features entry to collection index

[gdlol]

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

This devcontainer-config/features collection currently contains the 2 features below:

• user-init: Rename user with UID 1000 to remoteUser and setup XDG base directories.
• dot-config: Synchronize configuration files from .config/ to devcontainer workspaces.

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.