*Motivation*

Bump the development version to 2.6.0-SNAPSHOT

[pulsar-spark] upgrade SparkStreamingPulsarReceiver.java use pulsar-client and add spark example (#4143)

### Motivation

upgrade SparkStreamingPulsarReceiver.java use pulsar-client and add spark example

### Modifications

1. upgrade  SparkStreamingPulsarReceiver.java use pulsar-client, remove pulsar-client-1x pom
2. add  simple spark example

* After #3228, removed usages of deprecated client API

* Removed ProducerConfiguration from flink connector

* Use pulsar-client-1x in pulsar-spark

* Fixed log4j adapter

* Fixed flink examples

* Fixed storm integration tests

* Fixed storm example

* Wrapping message listeners in v1 lib wrapper

* Fixed unit tests

* Moved spark receiver test to test-containers to avoid shading issues

* Fixed PulsarAvroTableSinkTest

* Only run spark receiver test in integration tests

* removing metrics module from functions

* removing other references ot Prometheus metrics server

* removing references to pulsar-functions-metrics

* fix unit tests

* revert test change

* cleaning up and improving function metrics

* slight refactoring

* fix unittest

* moving pulsar-spark tests into its own module

* Removed shading relocations for Circe-checksum and lz4 libraries

* Also remove the jni shading in pulsar-broker-shaded

* Removed remaining relocations directives

* Moved Kafka wrapper tests to integration tests

* Do not shade io.netty.buffer.ByteBuf since it's passed between components

* Fixed presto dependencies license file

* adding a module that shades managed-ledger

* removing commented out lines

Signed-off-by: NSijie Guo <sijie@apache.org>

* Updates headers with ASF source files header

* change license to additional files