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

oci/authn_test.go

@@ -3,6 +3,7 @@
 package oci_test
 
 import (
+	"context"
 	"testing"
 
 	"github.com/docker/attest/internal/test"
@@ -20,11 +21,12 @@ func TestRegistryAuth(t *testing.T) {
 		{Image: "175142243308.dkr.ecr.us-east-1.amazonaws.com/e2e-test-image:latest"},
 		{Image: "docker/image-signer-verifier-test:latest"},
 	}
+	ctx := context.Background()
 	for _, tc := range testCases {
 		t.Run(tc.Image, func(t *testing.T) {
-			err := oci.PushIndexToRegistry(attIdx.Index, tc.Image)
+			err := oci.PushIndexToRegistry(ctx, attIdx.Index, tc.Image)
 			require.NoError(t, err)
-			_, err = oci.IndexFromRemote(tc.Image)
+			_, err = oci.IndexFromRemote(ctx, tc.Image)
 			require.NoError(t, err)
 		})
 	}