add scaling to Docker Compose setup

[tomkralidis]

Overview

Adds docker/compose/docker-compose.scale.yml to Docker Compose examples.

Related Issue / Discussion

None

Additional Information

None

Contributions and Licensing

(as per https://github.com/geopython/pycsw/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pycsw. I confirm that my contributions to pycsw will be compatible with the pycsw license guidelines at the time of contribution.
• I have already previously agreed to the pycsw Contributions and Licensing Guidelines

[tomkralidis]

CI failures are unrelated.