[BUG] Make default metadata columns and queue buffer size properties available through the public server settings

[mefrehner]

Describe the bug
When logged in as a user that has channel-related permissions but does not have the permission to view system settings, you will see an error message when attempting to create a new channel, although the channel will still be saved. This happens because in the ChannelSetup class, it retrieves the system settings to get the default metadata columns and the queue buffer size. To address this issue, we can add those properties to the PublicServerSettings class, which does not require any permissions to retrieve.

Expected behavior
Default metadata columns and queue buffer size properties are added to the PublicServerSettings
Users without the permission to view server settings no longer see an error message when creating or editing a channel

Actual behavior
When logged in as a user that has channel-related permissions but does not have the permission to view system settings, you will see an error message when attempting to create a new channel, although the channel will still be saved.

Additional context
Default metadata columns and queue buffer size properties are added to the PublicServerSettings