Support Channel properties which are not back by a ChannelInfo interface

ChannelInfo settings are being stored below the hst channel info node, for example

hst:workspace/hst:channel/hst:channelinfo

as a set of String, Boolean, Date, etc properties.

When the channel settings are read, at this moment, only the properties are read which are described by a ChannelInfo interface getter, which typically looks for example like:

@FieldGroupList({
        @FieldGroup(
                titleKey = "fields.channel",
                value = { "logo", "pageTitlePrefix" }
        )
})
public interface MobileInfo extends ChannelInfo {
    @Parameter(name = "logo", displayName = "Logo")
    @JcrPath(
            pickerSelectableNodeTypes = { "hippogogreengallery:imageset" },
            pickerInitialPath = "/content/gallery/logos"
    )
    String getLogoPath();

    @Parameter(name = "pageTitlePrefix", displayName = "Page title prefix", defaultValue = "Hippo Go Green")
    String getPageTitlePrefix();

Next to the primary ChannelInfo class for an hst:channel node we also support channel info mixin classes.

Any stored property on the hst:channelinfo node which is NOT represented by a ChannelInfo @Parameter is ignored.

When writing / updating the Channel Settings, any property that is already stored on the hst:channelinfo node but not represented by a ChannelInfo @Parameter is even removed.

The above is really unhandy: As a developer, I'd like to be able to bootstrap or configure channelinfo properties (settings) which are not editable or meant for the channel settings dialog, and I do not want these properties to be removed on save and I do want these properties to be available in the channel properties map.

A direct use case is for example to be able to configure the

org.hippoecm.hst.configuration.channel.PreviewURLChannelInfo_url

on channel info node without requiring a channel info interface for it