docs: better git error reporting

[Winand]

I use gitlab-ci-local inside Docker container on Windows, but the problem is not about Docker!

I've noted strange messages wih some repositories:

Using fallback git commit data
Unable to retrieve default remote branch, falling back to `main`.
Using fallback git remote data

And also .gitignore is.... ignored in those repos.

I checked the file git-data.ts and then tried to run git commands manually. I've found out that the problem is with ownership of .git folder when it is mounted inside Docker container: "detected dubious ownership in repository".

Expected behavior
It was not easy to identify this problem so I'd like to see extended error info in console on Git errors.

Host information
Windows 10
Docker Desktop
gitlab-ci-local 4.61.0

[firecow]

We are not supporting calling gitlab-ci-local from inside a docker container unfortunately.

But make sure your container is started with -u "$(id -u):$(id -g)" command, maybe that will solve the permission issues.

[Winand]

@firecow of course I understand that running GCL inside Docker is a special case and you don't have to support it officially!

I want to say that it would be nice to have better error reporting in git-data.ts. This problem has nothing to do with Docker.

For example initCommitData calls git rev-parse HEAD but on error I just see "Using fallback git commit data" in console without providing a reason for that.