chore: add OpenSSF Scorecard (#76)

Author: scop

.github/workflows/scorecard.yaml

@@ -0,0 +1,21 @@
+name: Scorecard
+on:
+  branch_protection_rule:
+  schedule:
+    - cron: "42 4 * * MON"
+  push:
+    branches:
+      - main
+
+permissions: {}
+
+jobs:
+  scorecard:
+    name: Scorecard
+    permissions:
+      contents: read
+      id-token: write
+      security-events: write
+    uses: UpCloudLtd/workflows/.github/workflows/openssf-scorecard.yaml@main
+    with:
+      publish-results: true

README.md

@@ -2,6 +2,7 @@
 
 ![Build Status](https://github.com/UpCloudLtd/packer-plugin-upcloud/workflows/test/badge.svg)
 ![Release Status](https://github.com/UpCloudLtd/packer-plugin-upcloud/workflows/release/badge.svg)
+[![OpenSSF Scorecard](https://api.scorecard.dev/projects/github.com/UpCloudLtd/packer-plugin-upcloud/badge)](https://scorecard.dev/viewer/?uri=github.com%2FUpCloudLtd%2Fpacker-plugin-upcloud)
 
 This is a builder plugin for Packer which can be used to generate storage templates on UpCloud. It utilises the [UpCloud Go API](https://github.com/UpCloudLtd/upcloud-go-api) to interface with the UpCloud API.