Add Swift Dockerfile to GitLab templates

changelogs/unreleased/dockerfile_swift_template.yml

+---
+title: "Add Swift Dockerfile to GitLab templates"
+merge_request: 28035
+author:
+type: added

doc/api/templates/dockerfiles.md

@@ -91,6 +91,10 @@ Example response:
   {
     "key": "Ruby-alpine",
     "name": "Ruby-alpine"
+  },
+  {
+    "key": "Swift",
+    "name": "Swift"
   }
 ]
 ```

vendor/Dockerfile/Swift.Dockerfile

+FROM swift:5.0 as builder
+
+WORKDIR /src
+COPY . .
+RUN swift build -c release
+
+FROM swift:5.0-slim
+
+WORKDIR /src
+COPY --from=builder /src .
+EXPOSE 8080
+
+CMD [ ".build/release/app"]