github: add code coverage with codecov.io (#6676)

.github/codecov.yml

@@ -0,0 +1,16 @@
+coverage:
+  status:
+    patch:
+      default:
+        target: "80"
+    project:
+      default:
+        target: auto
+        threshold: 1
+ignore:
+  - "test/"
+  - "benchmark/"
+  - "internal/testutils"
+  - ".*.pb.go"
+comment:
+  layout: "header"

.github/workflows/coverage.yml

@@ -0,0 +1,19 @@
+name: codecov
+on: [push, pull_request]
+jobs:
+  upload:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install checkout
+        uses: actions/checkout@v4
+
+      - name: Install checkout
+        uses: actions/setup-go@v4
+        with:
+          go-version: "stable"
+
+      - name: Run coverage
+        run: go test -coverprofile=coverage.out -coverpkg=./... ./...
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v3

README.md

@@ -3,6 +3,7 @@
 [![Build Status](https://travis-ci.org/grpc/grpc-go.svg)](https://travis-ci.org/grpc/grpc-go)
 [![GoDoc](https://pkg.go.dev/badge/google.golang.org/grpc)][API]
 [![GoReportCard](https://goreportcard.com/badge/grpc/grpc-go)](https://goreportcard.com/report/github.com/grpc/grpc-go)
+[![codecov](https://codecov.io/gh/{{REPOSITORY}}/branch/main/graph/badge.svg)](https://codecov.io/gh/{{REPOSITORY}})
 
 The [Go][] implementation of [gRPC][]: A high performance, open source, general
 RPC framework that puts mobile and HTTP/2 first. For more information see the