Updates to Java 17 for building

[onobc]

This proposal updates to Java 17 for building but retains Java 8 as the language level via the options.release flag.

The second commit takes advantage of the first and updates the spring javaformat to 0.0.42 (which relies on Java 17 compilation).

[lhotari]

There are 2 commits on purpose - please don't squash on commit.

squashing is currently forced by .asf.yaml settings. We would have to modify

pulsar-client-reactive/.asf.yaml

Lines 36 to 42 in 11b0de9

	enabled_merge_buttons:
	# enable squash button:
	squash: true
	# disable merge button:
	merge: false
	# disable rebase button:
	rebase: false

to enable merging without squashing.
Docs for .asf.yaml are at https://github.com/apache/infrastructure-asfyaml?tab=readme-ov-file#merge . We can change .asf.yaml for pulsar-client-reactive in a PR if we prefer to change the current settings.

[onobc]

There are 2 commits on purpose - please don't squash on commit.

squashing is currently forced by .asf.yaml settings. We would have to modify

pulsar-client-reactive/.asf.yaml

Lines 36 to 42 in 11b0de9

	enabled_merge_buttons:
	# enable squash button:
	squash: true
	# disable merge button:
	merge: false
	# disable rebase button:
	rebase: false

to enable merging without squashing.
Docs for .asf.yaml are at https://github.com/apache/infrastructure-asfyaml?tab=readme-ov-file#merge . We can change .asf.yaml for pulsar-client-reactive in a PR if we prefer to change the current settings.

Oh no, thats fine. This is not that important to split into 2 separate commits. We can just squash. In fact I will do that now as I am going to back off the version bump in subsequent commit.