feat: add fallback value for janus-idp.hostname for openshift clusters

[Zaperex]

Description of the change

Adds a fallback value for janus-idp.hostname for openshift clusters when both global.host and global.clusterRouterBase are not provided.

Existing or Associated Issue(s)

Fixes #167

Additional Information

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md. The pre-commit utility can be used to generate the necessary content. Use pre-commit run -a to apply changes.
• JSON Schema template updated and re-generated the raw schema via pre-commit hook.
• List tests pass for Chart using the Chart Testing tool and the ct lint command.

[masayag]

Thank you @Zaperex

[masayag]

@Zaperex any updates for this PR?

[rm3l]

One last thing: the default value for global.clusterRouterBase is apps.example.com, which means that if I want to use this new feature, I need to explicitly set it to an empty string in my values.yaml file, right?
Would it make sense to set the default value to an empty string instead, so that most users won´t even need to think about this? On OpenShift, without having to set global.clusterRouterBase, I would get the right hostname value.

[Zaperex]

whoops it seems the test charts github action isn't running in an openshift cluster, which is why it's failing with the new default value for global.clusterRouterBase

[openshift-ci]

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This pull-request has been approved by: rm3l

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