Prior to this commit, the `JmsTemplate` would use `MessagePostProcessor`
for mutating JMS messages before they are being sent, but only if the
method takes a post processor as an argument.
The main use case so far is to mutate messages after they've been
created by a `MessageConverter` from a payload.
This commit updates the `JmsClient` to use `MessagePostProcessor` more
broadly, for all outgoing messages (converted or not). This brings an
interception-like mechanism for clients to enrich the message before
being sent.
This change also updates the `JmsClient` static factories and
introduces a Builder, allowing for more configuration options: multiple
message converters and message post processors.
Closes gh-35271
ec87d90c9b