Add Page.GitInfo support for content from Git modules

Use blobless git clone (--filter=blob:none --no-checkout) to fetch
commit history for content from Git modules, then map it using the
existing gitmap library.  Cloned repos are cached in the modulegitinfo file cache.

Closes #14431
Fixes #5533

modules/module.go

@@ -79,6 +79,17 @@ type Module interface {
 
 	// Whether this module's dir is a watch candidate.
 	Watch() bool
+
+	// Origin returns the module's origin info if available (VCS, URL, Hash, etc.).
+	Origin() ModuleOrigin
+}
+
+// ModuleOrigin contains origin info for a Go module.
+type ModuleOrigin struct {
+	VCS  string // version control system, e.g. "git"
+	URL  string // repository URL, e.g. "https://github.com/bep/hugo-testing-git-versions"
+	Hash string // commit hash
+	Ref  string // e.g. "refs/tags/v3.0.1"
 }
 
 type Modules []Module
@@ -219,3 +230,15 @@ func (m *moduleAdapter) Watch() bool {
 	// That leaves modules inside the read-only module cache.
 	return !m.gomod.Indirect
 }
+
+func (m *moduleAdapter) Origin() ModuleOrigin {
+	if !m.IsGoMod() || m.gomod.Origin == nil {
+		return ModuleOrigin{}
+	}
+	return ModuleOrigin{
+		VCS:  m.gomod.Origin.VCS,
+		URL:  m.gomod.Origin.URL,
+		Hash: m.gomod.Origin.Hash,
+		Ref:  m.gomod.Origin.Ref,
+	}
+}