Update codecov config to support commenting code coverage in PRs

Add missing directory fixing go.etcd.io/etcd/etcdutl/v3/::etcdutl/

Note: we have some of the tests written in a way that is
non-deterministic across runs, thus, even when there is no code changes
there might still have slight variation for test coverage [2]

Reference:
[1] etcd-io#18131
[2] https://docs.codecov.com/docs/unexpected-coverage-changes#reasons-for-indirect-changes

Signed-off-by: Chun-Hung Tseng <[email protected]>

.github/workflows/coverage.yaml

@@ -1,9 +1,11 @@
 ---
 name: Coverage
-on: [push]
+on: [push, pull_request]
 permissions: read-all
 jobs:
   coverage:
+    # this is to prevent the job to run at forked projects
+    if: github.repository == 'etcd-io/etcd'
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false

codecov.yml

@@ -1,16 +1,32 @@
 ---
+# https://docs.codecov.com/docs/codecovyml-reference
 codecov:
   token: 6040de41-c073-4d6f-bbf8-d89256ef31e1
   disable_default_path_fixes: true
+  require_ci_to_pass: false
+  notify:
+    wait_for_ci: false
 fixes:
   - go.etcd.io/etcd/api/v3/::api/
   - go.etcd.io/etcd/client/v3/::client/v3/
   - go.etcd.io/etcd/client/v2/::client/v2/
   - go.etcd.io/etcd/etcdctl/v3/::etcdctl/
+  - go.etcd.io/etcd/etcdutl/v3/::etcdutl/
   - go.etcd.io/etcd/pkg/v3/::pkg/
   - go.etcd.io/etcd/server/v3/::server/
 ignore:
   - '**/*.pb.go'
   - '**/*.pb.gw.go'
   - tests/**/*
   - go.etcd.io/etcd/tests/**/*
+coverage:
+  range: 60..80
+  round: down
+  precision: 2
+comment:
+  layout: "header, files, diff, footer"
+  behavior: default # default: update, if exists. Otherwise post new; new: delete old and post new
+  require_changes: false # if true: only post the comment if coverage changes
+  require_base: false # [true :: must have a base report to post]
+  require_head: true # [true :: must have a head report to post]
+  hide_project_coverage: false # [true :: only show coverage on the git diff]