Adapt Helm chart to changes from #1572

[adutra]

Is your feature request related to a problem? Please describe.

The property names under polaris.features has changed lately with #1572. In particular, the word .defaults. has been removed.

However the Helm chart still displays two distinct sections, defaults and realmOverrides:

polaris/helm/polaris/values.yaml

Lines 507 to 521 in f4ecb6c

	features:
	# -- Features to enable or disable globally. If a feature is not present in the map, the default
	# built-in value is used.
	defaults: {}
	# ENFORCE_PRINCIPAL_CREDENTIAL_ROTATION_REQUIRED_CHECKING: false
	# SUPPORTED_CATALOG_STORAGE_TYPES:
	# - S3
	# - GCS
	# - AZURE
	# - FILE
	# -- Features to enable or disable per realm. This field is a map of maps. The realm name is the key, and the value is a map of
	# feature names to values. If a feature is not present in the map, the default value from the 'defaults' field is used.
	realmOverrides: {}
	# my-realm:
	# ENFORCE_PRINCIPAL_CREDENTIAL_ROTATION_REQUIRED_CHECKING: true

Describe the solution you'd like

It would be good to change that section to reflect the new property naming convention.

\cc @eric-maynard

Describe alternatives you've considered

No response

Additional context

No response

[snazy]

Helm-CI's consistently failing with this exception:

Caused by: java.lang.IllegalArgumentException: Unsupported feature configuration JSON type: OBJECT
	at org.apache.polaris.service.config.FeaturesConfiguration.configValue(FeaturesConfiguration.java:86)
	at org.apache.polaris.service.config.FeaturesConfiguration.convertMap(FeaturesConfiguration.java:59)
	at org.apache.polaris.service.config.FeaturesConfiguration.parseDefaults(FeaturesConfiguration.java:41)

It could be caused by the changes introduced by #1572. I suspect that that code now gets everything underneath polaris.features and then in consequence fails.

[adutra]

The current configmap contains these invalid entries:

    polaris.features."defaults"={}
    polaris.features."realmOverrides"={}