Add support for Fulcio and Rekor, and --sign-by-sigstore=param-file

(skopeo copy) and (skopeo sync) now support --sign-by-sigstore=param-file,
using the containers-sigstore-signing-params.yaml(5) file format.

That notably adds support for Fulcio and Rekor signing.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/golang.org/x/oauth2/README.md

@@ -0,0 +1,36 @@
+# OAuth2 for Go
+
+[![Go Reference](https://pkg.go.dev/badge/golang.org/x/oauth2.svg)](https://pkg.go.dev/golang.org/x/oauth2)
+[![Build Status](https://travis-ci.org/golang/oauth2.svg?branch=master)](https://travis-ci.org/golang/oauth2)
+
+oauth2 package contains a client implementation for OAuth 2.0 spec.
+
+## Installation
+
+~~~~
+go get golang.org/x/oauth2
+~~~~
+
+Or you can manually git clone the repository to
+`$(go env GOPATH)/src/golang.org/x/oauth2`.
+
+See pkg.go.dev for further documentation and examples.
+
+* [pkg.go.dev/golang.org/x/oauth2](https://pkg.go.dev/golang.org/x/oauth2)
+* [pkg.go.dev/golang.org/x/oauth2/google](https://pkg.go.dev/golang.org/x/oauth2/google)
+
+## Policy for new packages
+
+We no longer accept new provider-specific packages in this repo if all
+they do is add a single endpoint variable. If you just want to add a
+single endpoint, add it to the
+[pkg.go.dev/golang.org/x/oauth2/endpoints](https://pkg.go.dev/golang.org/x/oauth2/endpoints)
+package.
+
+## Report Issues / Send Patches
+
+This repository uses Gerrit for code changes. To learn how to submit changes to
+this repository, see https://golang.org/doc/contribute.html.
+
+The main issue tracker for the oauth2 repository is located at
+https://github.com/golang/oauth2/issues.