Allow using spring's object mapper

[worldtiki]

Description

This PR provides a simplified approach to customizing ObjectMapper beans used by Spring AI for JSON parsing operations, addressing feedback from PR #4833.

Problem

Issue #2494 identified several JSON parsing problems when using Spring AI with LLM-generated content such as unescaped control characters or date serialisation mismatch.
Users cannot configure Jackson features for their specific needs

Proposal

This PR refactors JsonParser and ModelOptionsUtils to support ObjectMapper injection through Spring's auto-configuration, allowing users to easily customise JSON processing behaviour.

Usage

@Configuration
public class MyJsonConfig {

    @Bean
    public ObjectMapper jsonParserObjectMapper() {
        return JsonMapper.builder()
            .disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
            .enable(SerializationFeature.INDENT_OUTPUT)
            // ... custom configuration
            .build();
    }
}

[ericbottard]

Hi @worldtiki,

thanks for your contribution!

While I can appreciate the need to provide means to customize ObjectMappers used in Spring AI, this PR seems too "overengineered" to me. IMO, there is no need for a dedicated maven module and autoconfiguration class for this. A change to existing configuration should hopefully suffice, keeping the approach of naming the OM beans.

Moreover, introducing ConfigurationProperties to drive the configuration of the OM is overkill. It merely reproduces what Jackson already provides and limits the configuration to what you've provided here. Just let users define their own OM bean if they want to, leveraging every Jackson feature they want if needed.

Lastly, I shall mention that complexifying the Jackson story in Spring AI before we migrate to Spring 7 / Boot 4 (which uses Jackson 3) may not be the best timing, so we should be very careful to not make things more complicated than they need be.

[worldtiki]

Yeap that's fair @ericbottard.
Let me take a second look and try to simplify this.