ci(docker): improve smoke test

[dargmuesli]

This pull request refactors the .github/smoke-test.sh script to simplify container and network naming, improve environment variable handling, and enhance error handling and messaging. The main changes make the script more robust and easier to maintain.

Container and network naming simplification:

• Renamed Docker containers and network from postgraphile-smoke/postgraphile-smoke-db to smoke/smoke-db, and the network from postgraphile-smoke to smoke.

Environment variable management improvements:

• Replaced the hardcoded env-vars directory with a dynamically created temporary directory (ENV_DIR) for environment variables, and updated all references accordingly.
• Updated cleanup logic to remove the temporary environment directory only if it was created.

Robustness and error handling:

• Improved Docker network creation by checking for existence before creating.
• Enhanced health check logic to handle containers without a HEALTHCHECK and provide clearer error messages and logs on failure.
• Updated curl command to include a timeout and improved error handling for failed requests.

Messaging and logging:

• Updated log and status messages to reflect new container names and clarify output.

[Copilot]

Pull request overview

Refactors the GitHub Actions Docker smoke test script to be more robust and maintainable by simplifying Docker resource naming, improving environment-variable file handling, and strengthening health check and request diagnostics.

Changes:

• Simplifies container/network naming to smoke, smoke-db, and smoke.
• Switches env-var file staging to a temporary directory (mktemp -d) and cleans it up on exit.
• Improves container health checking and adds a request timeout for the GraphQL probe.

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