[fix][broker] Validate per-[namespace][topic] entry filters

[nicoloboschi]

Motivation

When setting entry filters for namespace/topic there's no check that the entry filters exist and were correctly loaded by the broker. Since the actual entry filters classloaders are loaded in an async way, it's possible to corrupt the entry filters in the policies (it gets back to the broker config) returning OK to the API call. The only way to detect the entry filters is not working it's to look at the broker log (since the GET api call will return the content of the policies).

Modifications

• During the POST method the entry filters are validated. Validated means the entry filter name exists in the broker.
• Fixed the GET method with applied=true that wasn't taking into account the global ´AllowOverrideEntryFilters´ broker flag. Also it was mixing sync/async operations

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[nicoloboschi]

/pulsarbot rerun-failure-checks