docs: refresh README badges (#3164)

Drop the Go Report Card badge (the service is retired and the badge
now reads "retired"), use the official pkg.go.dev badge, and add
OpenSSF Scorecard and GitHub Sponsors badges.

Claude-Session: https://claude.ai/code/session_01QKDYQr53zNKkR7nif2CAAq

Author: vishr

README.md

@@ -1,9 +1,10 @@
 [![Latest release](https://img.shields.io/github/v/release/labstack/echo?style=flat-square&label=release&color=00afd1)](https://github.com/labstack/echo/releases)
 [![Last commit](https://img.shields.io/github/last-commit/labstack/echo/master?style=flat-square)](https://github.com/labstack/echo/commits/master)
-[![Go Reference](https://img.shields.io/badge/go-reference-blue.svg?style=flat-square)](https://pkg.go.dev/github.com/labstack/echo/v5)
-[![Go Report Card](https://goreportcard.com/badge/github.com/labstack/echo?style=flat-square)](https://goreportcard.com/report/github.com/labstack/echo)
+[![Go Reference](https://pkg.go.dev/badge/github.com/labstack/echo/v5.svg)](https://pkg.go.dev/github.com/labstack/echo/v5)
 [![CI](https://img.shields.io/github/actions/workflow/status/labstack/echo/ci.yml?style=flat-square&label=ci)](https://github.com/labstack/echo/actions/workflows/ci.yml)
 [![Codecov](https://img.shields.io/codecov/c/github/labstack/echo.svg?style=flat-square)](https://codecov.io/gh/labstack/echo)
+[![OpenSSF Scorecard](https://img.shields.io/ossf-scorecard/github.com/labstack/echo?style=flat-square&label=openssf%20scorecard)](https://scorecard.dev/viewer/?uri=github.com/labstack/echo)
+[![Sponsors](https://img.shields.io/github/sponsors/labstack?style=flat-square&color=db61a2)](https://github.com/sponsors/labstack)
 [![Discussions](https://img.shields.io/badge/community-discussions-00afd1.svg?style=flat-square)](https://github.com/labstack/echo/discussions)
 [![X](https://img.shields.io/badge/x-@labstack-000000.svg?style=flat-square)](https://x.com/labstack)
 [![License](https://img.shields.io/badge/license-mit-blue.svg?style=flat-square)](https://github.com/labstack/echo/blob/master/LICENSE)