Add references to environment variable docs and setup configuration docs for all components

[stevenbal]

Discussed with @alextreme, it would be useful to have links to the envvar docs (e.g. https://open-zaak.readthedocs.io/en/stable/installation/config/env_config.html) and setup configuration docs (e.g. https://open-zaak.readthedocs.io/en/stable/installation/config/openzaak_config_cli.html) in the READMEs of the charts.

READMEs for other charts (e.g. Open Inwoner https://github.com/maykinmedia/charts/tree/main/charts/openinwoner#configuration-and-installation-details) already have a reference to setup configuration

• Open Zaak 📝 [#350] add docs references to readme #351
• Open Notificaties 📝 [#350] add docs references to readme opennotificaties #359
• Objects API 📝 [#350] add docs references to readme objecten #363
• Objecttypes API https://github.com/maykinmedia/charts/pull/364/changes
• Open Klant 📝 [#350] add docs references to readme openklant #360
• Referentielijsten 📝 [#350] add docs references to readme referentielijsten #361
• Open Product 📝 [#350] add docs references to readme open-product #362
• Open Organisatie - Implemented in: Initial commit Open Organisatie helm chart #344