Removed checked exceptions from framework APIs

[onobc]

As pointed out by @jonasgeiregat in #546, the checked exception on PulsarTemplate.send* is not consistent w/ other Spring templates and forces users to catch PulsarClientException always.

Let's instead return a runtime variant of PulsarClientException.

[jonas-grgt]

Was also considering to remove PulsarClientException from PulsarProducerFactory as it had the same inconvenient effect.

[onobc]

Was also considering to remove PulsarClientException from PulsarProducerFactory as it had the same inconvenient effect.

Agreed. In general, "favor unchecked exception over checked exception" is the theme and I am in favor of doing this in the PPF as well.