update configuration to YAML

[tomkralidis]

Overview

Updates pycsw configuration from ini to YAML.

Related Issue / Discussion

Fixes #797

Additional Information

TODO

• migration tool/script

External updates required

• pycsw public demo (https://github.com/geopython/demo.pycsw.org)
• GeoNode CSW plugin
• CKAN CSW plugin

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

[kalxas]

We will also need to update the kubernetes helm charts when this is merged

[tomkralidis]

k8s and helm charts first pass updated as part of this PR.

[tomkralidis]

• migration script added
• associated demo update PR in update configuration to YAML demo.pycsw.org#10

[kalxas]

Excellent work!

[pvgenuchten]

Nice work, just to confirm: the override mechanism with environmental variables is still supported?

[tomkralidis]

@pvgenuchten yes, environment variables are interpreted as per before.