feat: allow configuring a custom JsonMapper

[sonallux]

This PR adjust the definition of the JsonMapper bean in the ContextFunctionCatalogAutoConfiguration to be conditional on missing bean, so a custom JsonMapper can be registered and used with spring-cloud-functions.

This PR fixes #1159 and fixes #1059.

[olegz]

I am trying to understand the purpose for this. JsonMapper is just a wrapper class over ObjectMapper or Gson, so don't you think it would be better to address it by injecting an instance of one of those? I know it can't be done now, but thinking that we could. Can you please elaborate about the problem you are trying to solve?

[sonallux]

I am trying to understand the purpose for this. JsonMapper is just a wrapper class over ObjectMapper or Gson, so don't you think it would be better to address it by injecting an instance of one of those? I know it can't be done now, but thinking that we could. Can you please elaborate about the problem you are trying to solve?

@olegz I just wanted to fix issue #1159 and it seemed reasonable to allow providing a custom JsonMapper bean. Yes allowing to inject the json implementation would be better. The other PR #1162 is implementing this behaviour.

[olegz]

The #1162 has been merged and I honestly prefer this approach, so please let me know if that's ok with you so I can close this

[sonallux]

The #1162 has been merged and I honestly prefer this approach, so please let me know if that's ok with you so I can close this

I am perfectly fine with this, so I am closing my PR.

[Xyaren]

I request this to be expedited.
This issue is currently breaking non-default json serialization.