Add GitHub Action workflow for verifying pact tests

This moves the pact verification to a GitHub Action and will no longer
be performed by a Jenkins build. This workflow will also be called by
GDS API Adapters as part of it's CI build to assert that newly generated
pacts are valid against this app. To avoid running this same task twice
`pact:verify` is no longer part of the Jenkins test actions and instead
the other rake default steps are included.

For more details see alphagov/gds-api-adapters#1175

.github/workflows/pact-verify.yml

@@ -0,0 +1,49 @@
+# Pact verify workflow
+#
+# This workflow asserts that Pact contract tests are valid against this
+# codebase. It is trigged when changes are made to this project and it
+# is explicitly called by GDS API Adapters when changes are made there.
+on:
+  pull_request:
+  push:
+  workflow_call:
+    inputs:
+      # what branch or Git SHA to clone this app with, only applies when
+      # called as a workflow, so current commit applies to push/pull requests
+      commitish:
+        required: false
+        type: string
+        default: main
+      pact_consumer_version:
+        required: true
+        type: string
+
+jobs:
+  pact_verify:
+    name: Verify pact tests
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:13
+        ports: ["5432:5432"]
+        env:
+          POSTGRES_HOST_AUTH_METHOD: trust
+        options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5
+      redis:
+        image: redis
+        ports: ["6379:6379"]
+        options: --health-cmd "redis-cli ping" --health-interval 10s --health-timeout 5s --health-retries 5
+    env:
+      PACT_CONSUMER_VERSION: ${{ inputs.pact_consumer_version || 'branch-main' }}
+      TEST_DATABASE_URL: postgresql://postgres@localhost/test-db
+      RAILS_ENV: test
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          repository: alphagov/email-alert-api
+          ref: ${{ inputs.commitish || github.sha }}
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+      - run: bundle exec rails db:setup
+      - run: bundle exec rake pact:verify

Jenkinsfile

@@ -4,5 +4,7 @@ library("govuk")
 
 node {
   govuk.setEnvar("TEST_DATABASE_URL", "postgresql://postgres@127.0.0.1:54313/email-alert-api-test")
-  govuk.buildProject()
+  govuk.buildProject(
+    overrideTestTask: { sh("bundle exec rake lint spec") }
+  )
 }