Syft Directory Source: Git Tag and Metadata Information

**What would you like to be added**:
When syft runs a directory scan it should be able to intuition when it is in a git repository.

This would then lead for commit sha, tag and other git metadata to be amended to the source object of the SBOM.

**Why is this needed**:
This information can be carried forward into grype scanning and other templates/vulnerability reports to provide more accurate labeling and pinpointing of which version of a software project and SBOM was generated against.

**Additional context**:
Picking this issue up means editing the `Source` object and adding a specific Metadata surrounding the new git data points:
https://github.com/anchore/syft/blob/1c37bab2b2b45f59ab7a9b70e3a200206771996e/syft/format/syftjson/model/source.go#L15

Start with syft/format/syftjson/model/source.go and review the existing Source object. Trace how directory scans populate that object, then determine how git repository metadata should be represented and carried into the SBOM. Done means directory scans include the agreed commit SHA, tag, and related git metadata without affecting non-git sources.

Written by the indexing model from the issue text.