Add Observations for send/receive

[onobc]

This adds observations to PulsarTemplate and DefaultPulsarMessageListenerContainer.

Remaining items (follow on PRs)

• auto-generate docs and plug-in to newly added observability section in ref guide
• add properties and hook into our Spring Boot starter where it makes sense (Support observations in Spring Boot starter #147)

Big thanks to @artembilan and @garyrussell for trailblazing this in spring-kafka as this was my reference model for this proposal.

@marcingrzejszczak @jonatan-ivanov if either of you get a chance to give this a once-over that would be great. However, I know that treatment was applied to spring-kafka and as stated above, this was modeled from that. I am fairly certain there will be no surprises here.

[marcingrzejszczak]

I don't know the details of how Pulsar works, but from the point of view of Observability this looks good :) I would love to see a Zipkin screenshot to confirm the tracing part.

[onobc]

I went ahead and added the auto-generated docs as a 2nd commit in this PR. Looks good...

[artembilan]

Why generated docs are missed from the commit?

[onobc]

Why generated docs are missed from the commit?

We have not been checking them in as the build creates them. Do you check them in SI and/or SK?

[artembilan]

Do you check them in SI ?

I do at the moment. Plus I also added a condition to not run that Gradle task on CI.
My point was that this doc eventually going to be "very static" when the code base will have settled.

Although I'll debate with myself if this really has to be deferred to the docs creation phase instead.

[onobc]

Do you check them in SI ?

I do at the moment. Plus I also added a condition to not run that Gradle task on CI. My point was that this doc eventually going to be "very static" when the code base will have settled.

Although I'll debate with myself if this really has to be deferred to the docs creation phase instead.

That would be a true optimization (dont' run during build if its 99% static content). However, if the tool picks up changes (would not happen automatically unless version was set to latest or snaphot though) we would not see those w/o manually running. Also, people may forget to run the docs generator when something changes. They would have to know what those change-worthy things are.

[artembilan]

Did you see Checkstyle failures:

Error: eckstyle] [ERROR] /home/runner/work/spring-pulsar/spring-pulsar/spring-pulsar/src/main/java/org/springframework/pulsar/observation/PulsarMessageSenderContext.java:74:9: Class MessageHolder should be declared as final. [FinalClass]

?

[onobc]

Did you see Checkstyle failures:

Yeh I did. I am going to squash/rebase a bit and will address then.

Error: eckstyle] [ERROR] /home/runner/work/spring-pulsar/spring-pulsar/spring-pulsar/src/main/java/org/springframework/pulsar/observation/PulsarMessageSenderContext.java:74:9: Class MessageHolder should be declared as final. [FinalClass]