Entry Filters: allow to configure the filters per namespace and not only globally

[eolivelli]

In PIP-105 we introduced Server side filters.
Now in 2.10 and 2.11 you can only configure the filters (entryFilterNames) in broker.conf.

A natural extension is to let the filters be configured per namespace.

Main reasons:

• different users/tenant may need different filters
• activating a filter on namespaces that don't need the filter is a waste of resources

Therefore we need a API to report to clients that a filter is present on the server, because this way the client may decide to perform some processing locally or let the broker do the processing.

Feature request:

• add per-namespace filters (or even per-topic)
• add an API to get the filters configured on the namespace (accessible with the same permissions needed to consume from the topic/namespace)