Add on-tag release pipeline to upload the provider to artifactapi

Publish the provider so it can be consumed from terraform-vault: on a tag,
package the linux_amd64 build into a versioned zip and PUT it to the artifactapi
terraform registry, mirroring terraform-provider-artifactapi's release flow.

- Add .woodpecker/release.yml (event: tag) running make package + curl upload to
  remotes/terraform-unkin/files/unkin/litellmvaultsecret/

.woodpecker/release.yml

@@ -0,0 +1,19 @@
+when:
+  - event: tag
+
+steps:
+  - name: package
+    image: git.unkin.net/unkin/almalinux9-gobuilder:20260606
+    commands:
+      - make package VERSION=${CI_COMMIT_TAG}
+
+  - name: upload
+    image: git.unkin.net/unkin/almalinux9-base:20260606
+    commands:
+      - |
+        VERSION=$$(echo ${CI_COMMIT_TAG} | sed 's/^v//')
+        FILE="terraform-provider-litellmvaultsecret_$${VERSION}_linux_amd64.zip"
+        curl -f -X PUT \
+          "https://artifactapi3.k8s.syd1.au.unkin.net/api/v2/remotes/terraform-unkin/files/unkin/litellmvaultsecret/$${FILE}" \
+          -H "Content-Type: application/zip" \
+          --data-binary @"$${FILE}"