feat: make substrait repo a go module (#712)

This facilitates substrait assets use in go projects

core.go

@@ -0,0 +1,14 @@
+// Package substrait provides access to Substrait artifacts via embed.FS.
+// Use substrait.GetSubstraitFS() to retrieve the embed.FS object.
+package substrait
+
+import "embed"
+
+// Add all directories which should be exposed in below
+//
+//go:embed extensions/*
+var substraitFS embed.FS
+
+func GetSubstraitFS() embed.FS {
+	return substraitFS
+}

go.mod

@@ -0,0 +1,3 @@
+module github.com/substrait-io/substrait
+
+go 1.22.0