Backport improvements around netty direct buffer pooling

[Tim-Brooks]

This commit backports 3 commits related to improving the story around
direct buffer pooling in netty.

Remove option to enable direct buffer pooling (#48310)

This commit removes the option to change the netty system properties to
reenable the direct buffer pooling. It also removes the need for us to
disable the buffer pooling in the system properties file. Instead, we
programmatically craete an allocator that is used by our networking
layer.

This commit does introduce an Elasticsearch property which allows the
user to fallback on the netty default allocator. If they choose this
option, they can configure the default allocator how they wish using the
standard netty properties.

Remove default netty allocator empty assertions (#48356)

This commit removes a problematic assertion that the netty default
allocator is not used. This assertion is problematic because any other
test can cause this task to fail by touching the default allocator. We
assert that we are using heap buffers in the channel.

Upgrade to Netty 4.1.43 (#48484)

With this update we can remove the mitigation in our custom allocator
which forces heap buffer allocations.

[elasticmachine]

Pinging @elastic/es-distributed (:Distributed/Network)