Add the dependabot PR unification workflow (open-telemetry#335)

Taken from
https://github.com/open-telemetry/opentelemetry-go-build-tools/blob/4e238e9c5b27995f884fee440d572ecf7018ca6c/.github/workflows/create-dependabot-pr.yml

.github/workflows/create-dependabot-pr.yml

@@ -0,0 +1,24 @@
+name: Automation - Dependabot PR
+
+on:
+  workflow_dispatch:
+
+jobs:
+  create-pr:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install zsh
+        run: sudo apt-get update; sudo apt-get install zsh
+
+      - name: Setup Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: "~1.21.1"
+          check-latest: true
+
+      - name: Run dependabot-pr.sh
+        run: ./.github/workflows/scripts/dependabot-pr.sh
+        env:
+          GITHUB_TOKEN: ${{ secrets.OPENTELEMETRYBOT_GITHUB_TOKEN }}

.github/workflows/scripts/dependabot-pr.sh

@@ -0,0 +1,61 @@
+#!/bin/zsh -ex
+
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+git config user.name opentelemetrybot
+git config user.email 107717825+opentelemetrybot@users.noreply.github.com
+
+PR_NAME=dependabot-prs/`date +'%Y-%m-%dT%H%M%S'`
+git checkout -b $PR_NAME
+
+IFS=$'\n'
+requests=($( gh pr list --search "author:app/dependabot" --json title --jq '.[].title' ))
+message=""
+dirs=(`find . -type f -name "go.mod" -exec dirname {} \; | sort | egrep  '^./'`)
+
+declare -A mods
+
+for line in $requests; do
+    echo $line
+    if [[ $line != Bump* ]]; then
+        continue
+    fi
+
+    module=$(echo $line | cut -f 2 -d " ")
+    version=$(echo $line | cut -f 6 -d " ")
+
+    mods[$module]=$version
+    message+=$line
+    message+=$'\n'
+done
+
+for module version in ${(kv)mods}; do
+    topdir=`pwd`
+    for dir in $dirs; do
+        echo "checking $dir"
+        cd $dir && if grep -q "$module " go.mod; then go get "$module"@v"$version"; fi
+        cd $topdir
+    done
+done
+
+make tidy lint build
+
+git add go.sum go.mod
+git add "**/go.sum" "**/go.mod"
+git commit -m "dependabot updates `date`
+$message"
+git push origin $PR_NAME
+
+gh pr create --title "[chore] dependabot updates `date`" --body "$message"