Change default behavior of `sentry.reactive.thread-local-accessor-enabled` to true

[ririnto]

Problem Statement

Currently, SentryWebfluxAutoConfiguration registers the legacy filter (SentryWebfluxFilterConfiguration) whenever the property sentry.reactive.thread-local-accessor-enabled is not set. As a result, users who omit that property miss out on the benefits of the newer ThreadLocalAccessor-based filter.

Changing the default to SentryWebfluxFilterThreadLocalAccessorConfiguration would allow more users to benefit from improved context propagation without extra configuration.

Solution Brainstorm

Sentry 8.0.0 release candidate is in progress, so this is a good time to adjust the default behavior.

I propose:

1. Add matchIfMissing = true to the @ConditionalOnProperty in SentryThreadLocalAccessorCondition.
2. Remove matchIfMissing = true from SentryDisableThreadLocalAccessorCondition.

This way, SentryWebfluxFilterThreadLocalAccessorConfiguration is used when sentry.reactive.thread-local-accessor-enabled is not explicitly defined.

Users who still prefer the legacy filter can explicitly set sentry.reactive.thread-local-accessor-enabled=false.

[ririnto]

Note.
The io.sentry.spring.boot.jakarta.SentryProperties$Reactive.threadLocalAccessorEnabled field is set to true by default, but this default value does not currently affect the condition (@ConditionalOnProperty).

As a result, when sentry.reactive.thread-local-accessor-enabled is not explicitly defined, the legacy filter (SentryWebfluxFilterConfiguration) is still registered.

[adinauer]

Thank you for opening this issue. I see no problem changing the default. I'll open a PR.

[adinauer]

We have just released https://github.com/getsentry/sentry-java/releases/tag/8.0.0-rc.4 which has the default changed. If you give it a try - feedback is very welcome.

[ririnto]

For the same reason, the 7.x version might require changes.

When building sentry-spring-jakarta, the Spring plugin generates the file additional-spring-configuration-metadata.json.

In this file, the default value of sentry.reactive.thread-local-accessor-enabled is set to true.

Therefore, you need to set SentryProperties.ThreadLocalAccessorEnabled to false (or `null). Alternatively, you can apply the same patch as in #4023.