feature!: support for setting HTTP User-Agent header (#157)

* feature!: support for setting HTTP User-Agent header

* fix lint

* fix e2e

* refactor: move http.go to internal/util/useragent package and rename functions to Get and Set

* Move packages and use attest version

internal/version/version.go

@@ -0,0 +1,39 @@
+package version
+
+import (
+	"fmt"
+	"runtime/debug"
+
+	"github.com/Masterminds/semver/v3"
+)
+
+const ThisModulePath = "github.com/docker/attest"
+
+// Get returns the version of the attest module.
+// this can return nil if the version can't be determined (without an error).
+func Get() (*semver.Version, error) {
+	var attestMod *debug.Module
+	bi, ok := debug.ReadBuildInfo()
+	if !ok {
+		return nil, nil
+	}
+	if bi.Main.Path == ThisModulePath {
+		attestMod = &bi.Main
+	} else {
+		for _, dep := range bi.Deps {
+			if dep.Path == ThisModulePath {
+				attestMod = dep
+				break
+			}
+		}
+	}
+	if attestMod == nil {
+		return nil, nil
+	}
+
+	attestVersion, err := semver.NewVersion(attestMod.Version)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse version %s: %w", attestMod.Version, err)
+	}
+	return attestVersion, nil
+}