feat(dev): allow running example app with docker

this PR allows backstage contributors to run the example app against
actual postgres, opensearch and redis services using docker and docker
compose file.

no changeset as this doesn't affect any published packages.

Signed-off-by: Hellgren Heikki <heikki.hellgren@op.fi>

package.json

@@ -53,6 +53,7 @@
     "snyk:test:package": "yarn snyk:test --include",
     "start": "backstage-cli repo start",
     "start-backend": "echo \"Use 'yarn start example-backend' instead\"",
+    "start:docker": "docker compose -f docker-compose.deps.yml up --wait && BACKSTAGE_ENV=docker yarn start",
     "start:microsite": "cd microsite/ && yarn start",
     "start:next": "yarn start example-app-next example-backend",
     "storybook": "storybook dev -p 6006",