Make git commit info optional and per-package in channel manifests
Make git commit info optional and per-package in channel manifests

At the moment it is always missing for Cargo and RLS.
Their respective build systems need to be modified to include
`git-commit-hash` files in their "dist" tarballs.

aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust