internal/upload: Add support for upload to GCP and CLI tool using it

Add new internal upload target for Google Cloud Platform and
osbuild-upload-gcp CLI tool which uses the API.

Supported features are:
- Authenticate with GCP using explicitly provided JSON credentials
  file or let the authentication be handled automatically by the
  Google cloud client library. The later is useful e.g. when the worker
  is running in GCP VM instance, which has associated permissions with
  it.
- Upload an existing image file into existing Storage bucket.
- Verify MD5 checksum of the uploaded image file against the local
  file's checksum.
- Import the uploaded image file into Compute Node as an Image.
- Delete the uploaded image file after a successful image import.
- Delete all cache files from storage created as part of the image
  import build job.
- Share the imported image with a list of specified accounts.

GCP-specific image type is not yet added, since GCP supports importing
VMDK and VHD images, which the osbuild-composer already supports.

Update go.mod, vendor/ content and SPEC file with new dependencies.

Signed-off-by: Tomas Hozza <thozza@redhat.com>

go.mod

@@ -3,6 +3,8 @@ module github.com/osbuild/osbuild-composer
 go 1.14
 
 require (
+	cloud.google.com/go v0.75.0
+	cloud.google.com/go/storage v1.10.0
 	github.com/Azure/azure-sdk-for-go v41.3.0+incompatible
 	github.com/Azure/azure-storage-blob-go v0.13.0
 	github.com/Azure/go-autorest/autorest v0.10.0
@@ -17,8 +19,9 @@ require (
 	github.com/getkin/kin-openapi v0.13.0
 	github.com/go-chi/chi v4.0.2+incompatible
 	github.com/gobwas/glob v0.2.3
-	github.com/google/go-cmp v0.3.1
-	github.com/google/uuid v1.1.1
+	github.com/golang/protobuf v1.4.3
+	github.com/google/go-cmp v0.5.4
+	github.com/google/uuid v1.1.2
 	github.com/gophercloud/gophercloud v0.11.0
 	github.com/julienschmidt/httprouter v1.2.0
 	github.com/kolo/xmlrpc v0.0.0-20200310150728-e0350524596b
@@ -26,6 +29,9 @@ require (
 	github.com/stretchr/testify v1.5.1
 	github.com/ubccr/kerby v0.0.0-20170626144437-201a958fc453
 	github.com/vmware/govmomi v0.23.0
-	golang.org/x/net v0.0.0-20200202094626-16171245cfb2 // indirect
-	golang.org/x/sys v0.0.0-20200828194041-157a740278f4
+	golang.org/x/oauth2 v0.0.0-20201208152858-08078c50e5b5
+	golang.org/x/sys v0.0.0-20201201145000-ef89a241ccb3
+	google.golang.org/api v0.36.0
+	google.golang.org/genproto v0.0.0-20210108203827-ffc7fda8c3d7
+	google.golang.org/protobuf v1.25.0
 )