collection-index.yml: add feature 'perl'

[haukex]

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

• none

Description

I would appreciate my feature collection to be added to the list. Currently, it only provides one feature, Perl development support, which as far as I can tell no other feature provides. I may add more features in the future.

Collection 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.