Keep non-ASCII characters in config output

[hdimer]

Fixes #1536.

podman-compose config renders any non-ASCII character in a compose value as a \xE9-style escape:

services:
  sample:
    image: nopush/podman-compose-test
    volumes:
    - /home/développement:/home/dev

$ podman-compose -f docker-compose.yaml config
services:
  sample:
    image: nopush/podman-compose-test
    volumes:
    - "/home/d\xE9veloppement:/home/dev"

The cause is yaml.safe_dump, which defaults to allow_unicode=False. Docker Compose prints
these characters literally. To be clear about the impact: the escaped form is valid YAML and
still parses back to the correct path, so this is a rendering/parity problem, not data loss.

I deliberately left the neighbouring json.dumps alone. It feeds self.yaml_hash, and changing
its encoding would change the hash used to decide whether containers need recreating.

One trade-off worth naming: the print in compose_config can now raise UnicodeEncodeError
if stdout is not UTF-8 capable, where before it silently emitted escapes. Docker Compose behaves
the same way and compose files are already read as UTF-8, so I left it alone, but I'm happy to
add handling if you'd rather.

Tests: a unit test covering the merged YAML, plus an exact-output integration test in
tests/integration/command_config/ alongside the existing config cases.

Written with AI assistance; reviewed and tested locally before submitting.