enable the use of a custom ObjectMapper

[jitokim]

fix: #723 using builder of JsonPulsarHeaderMapper.

AS-IS
JacksonUtils.enhancedObjectMapper() was always used.
JsonPulsarHeaderMapper.builder().build()

TO-BE
Inject ObjectMapper to builder in the constructor of AbstractPulsarMessageToSpringMessageAdapter
JsonPulsarHeaderMapper.builder().objectMapper(objectMapper).build()

By adding ObjectMapper to the constructor of AbstractPulsarMessageToSpringMessageAdapter, we enable the use of a custom ObjectMapper.

[onobc]

Thanks for the contribution @jitokim . The proposed changes would allow a user-provided object mapper only for Pulsar message headers JSON de/serialization. To allow a user-provided object mapper when de/serializing the message payload is a bit more complicated. I have a PR in progress to do this. What I will do is combine that PR w/ part of this PR. I will try to get something for review in the next few days. I will ping you when I do.

Thank you.

[jitokim]

I agree that allowing a user-provided object mapper for the message payload is complicated
Thank you for the review 😃

[onobc]

Hi @jitokim
I have used your initial code proposal as a starting point for #762.

1. Thank you for the reminder to implement this for the JSON headers.
2. Thank you for the great starting point.

You can see I tweaked it quite a bit, namely:

• now looking up of the ObjectMapper bean later than afterSingletonInstantiated as that is a bit too early to get access to the mapper
• lookup the mapper by special name pulsarHeaderObjectMapper
• added tests for @PulsarReader @PulsarListener, @ReactivePulsarListener
• added docs

I had intentions of keeping your original commit in my PR but it diverged enough that I did not go that route.
I would however like to give you the credit you deserve via a co-author on the new PR. If you agree can you reply here w/ the following info:

• Email address you want to use as the Co-Author (see
  https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors#required-co-author-information)

• Your first name + last name you want to use in the Javadoc @author tag for the classes that you originally modified (annotation post processors and listener endpoints).

Closing in favor of #762

[jitokim]

Hi, @onobc

Thank you so much for considering me and for the thoughtful acknowledgment.

For the information, I would like to use the following:
First name: Jihoon
Last name: Kim
Email address: [email protected]

I really appreciate the great open-source project you're creating.