Add Git Extended feature to collection index

[Agustin-Gigena]

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

Please replace this line with a description of your PR.

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 (must be the collection root, e.g. ghcr.io/<owner>/<repo> — one entry per repository, not one per Feature; do not include http:// or https://)
• I acknowledge that this collection provides new functionality, distinct from the existing collections part of this index.

[Kaniska244]

Hi @Agustin-Gigena

Thank you for your contribution. Since these features are all part of the same repo, could you combine these all into a single entry. I know it's a bit tricky for the title, but it reduces the cardinality of the features list.
Also the ORAS spec requires the ociReference to be in lower case. Would you kindly update the same.
The supporting tools do help convert the case, however, its better to sync as much as possible.