scripts: add script to measure percentage of commits with failed status

This is to start measuring the test flakiness and see the numbers improving once we improve and deflake flaky tests

Fixes etcd-io#13167

scripts/measure-test-flakiness.sh

@@ -0,0 +1,27 @@
+#!/bin/bash
+
+set -e
+set -o pipefail
+
+if [[ -z ${GITHUB_TOKEN} ]]
+then
+    echo "Please set the \$GITHUB_TOKEN environment variable for the script to work"
+    exit 1
+fi
+
+temp_dir=$(mktemp -d)
+
+trap '{ rm -rf -- "${temp_dir}"; }' EXIT
+
+json_file="${temp_dir}/commit-and-check-data.json"
+
+curl --fail --show-error --silent -H "Authorization: token ${GITHUB_TOKEN}" \
+    -X POST \
+    -d '{
+        "query": "query { repository(owner: \"etcd-io\", name: \"etcd\") { defaultBranchRef { target { ... on Commit { history(first: 100) { edges { node { ... on Commit { commitUrl statusCheckRollup { state } } } } } } } } } }"
+    }' \
+    https://api.github.com/graphql | jq . > "${json_file}"
+
+failure_percentage=$(jq '.data.repository.defaultBranchRef.target.history.edges | reduce .[] as $item (0; if $item.node.statusCheckRollup.state == "FAILURE" then (. + 1) else . end)' "${json_file}")
+
+echo "Commit status failure percentage is - ${failure_percentage} %"