JMSPublishFilter: improve memory footprint and impose a limit

[eolivelli]

Motivation:
The JMSPublishFilter can allocate an unbounded amount of memory (especially String objects), this can lead to OutOfMemory errors.

Changes:
This is a refactor that reduces the amount of memory retained to handle the queue of messages in the JMSPublishFilter.
Previously the queue contained MessageMetadata, with all the properties as Strings, now we keep only 1 Netty ByteBuf, and the parsing of the Metadata is done on the processing thread, 1 message at a time per subscription.

Therefore there is a limit on the amount of memory retained for the queue, when the limit is reached the producers start to be throttled.

• new metric (gauge): pulsar_jmsfilter_processing_memory: bytes used for MessageMetadata waiting for processing
• new metric (gauge): pulsar_jmsfilter_processing_pending_operations: number of pending operations
• new configuration: jmsFiltersOnPublishMaxMemoryMB, this is the maximum amount of memory to retain for the operations in the queue, this is heap memory