chore(ci): Add downstream merge trigger to github action (#3014)

.github/workflows/trigger-merge-to-downstream.yml

@@ -0,0 +1,24 @@
+name: trigger-merge-to-downstream
+
+on:
+  push:
+    branches:
+      - main
+      - release/**
+
+permssions:
+  contents: read
+
+jobs:
+  trigger-merge:
+    if: github.repository == 'hashicorp/boundary'
+    runs-on: ${{ fromJSON(vars.RUNNER) }}
+    env:
+      DOWNSTREAM_SLUG: ${{ vars.DOWNSTREAM_SLUG }}
+      DOWNSTREAM_TOK: ${{ secrets.DOWNSTREAM_TOK }}
+      DOWNSTREAM_WORKFLOW: ${{ vars.DOWNSTREAM_WORKFLOW }}
+    steps:
+      - uses: actions/checkout@v3
+      - name: Trigger Merge
+        run: |
+          ./scripts/trigger-merge-to-downstream-gha ${{ github.ref_name }}

scripts/trigger-merge-to-downstream-gha

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+
+BRANCH=${1}
+
+if [[ -z "${BRANCH}" ]]; then
+    echo "skipping no branch specified"
+    exit 0
+fi
+
+if [[ -z "${DOWNSTREAM_SLUG}" ]]; then
+    echo "skipping, no downstream"
+    exit 0
+fi
+
+if [[ -z ${DOWNSTREAM_TOK} ]]; then
+  exit 0
+fi
+
+if [[ -z ${DOWNSTREAM_WORKFLOW} ]]; then
+    echo "skipping, no downstream workflow"
+    exit 0
+fi
+
+curl \
+  --silent \
+  -X POST \
+  -H "Accept: application/vnd.github+json" \
+  -H "Authorization: Bearer ${DOWNSTREAM_TOK}" \
+  -H "X-GitHub-Api-Version: 2022-11-28" \
+  "https://api.github.com/repos/hashicorp/boundary-${DOWNSTREAM_SLUG}/actions/workflows/${DOWNSTREAM_WORKFLOW}/dispatches" \
+  -d @- << EOF
+{
+  "ref": "${BRANCH}",
+  "inputs": {
+    "from-branch": "${BRANCH}",
+    "to-branch": "${BRANCH}"
+  }
+}
+EOF