Add ziglang devcontainers template

[fardragon]

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)

Related Issues

• Related Issue #
• Closes #

Description

Adds ziglang devcontainers template.

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.

[fardragon]

@samruddhikhandale sorry for pinging you directly, but you seem to be the person approving things here most recently. Is there anything I can do to move this along?