Add Magento Open Source Dev Container Templates collection (#696)

Adds doughatcher/devcontainer-templates to the collection index.

This is the same collection that was originally proposed in PR #500
(closed when the work was donated to a corporate namespace). The OSS
variant is now back under doughatcher/ as a public, community-focused
template collection. The corporate variant has been archived.

Maintainer: Doug Hatcher
Repository: https://github.com/doughatcher/devcontainer-templates
OCI: ghcr.io/doughatcher/devcontainer-templates

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Abdurrahmaan Iqbal <abdurriq@github.com>

Author: 3 people

_data/collection-index.yml

@@ -1486,3 +1486,8 @@
   contact: https://github.com/mrhornsby/trunk-devcontainer-feature/issues
   repository: https://github.com/mrhornsby/trunk-devcontainer-feature
   ociReference: ghcr.io/mrhornsby/trunk-devcontainer-feature
+- name: Magento Open Source Dev Container Templates
+  maintainer: Doug Hatcher
+  contact: https://github.com/doughatcher/devcontainer-templates/issues
+  repository: https://github.com/doughatcher/devcontainer-templates
+  ociReference: ghcr.io/doughatcher/devcontainer-templates