Make JCacheCacheMeterBinderProvider back off when user provides a bean (fixes #46212)

[SSUday]

Problem:
Micrometer added an option to register JCache removals as a function counter.
In Boot, users cannot provide a custom JCacheCacheMeterBinderProvider because
our auto-configured provider wasn’t conditional on a user bean.

Solution:

• Annotate the auto-configured provider with @ConditionalOnMissingBean(JCacheCacheMeterBinderProvider.class)
• Add JCacheCacheMeterBinderProviderBackOffTests to prove a user bean is used.

Risk/Docs:

• Backwards-compatible; only changes selection order.
• No docs changes needed.

Fixes #46212

[snicoll]

Thanks for the PR but it isn't actionable. The issue you've referenced is pending design work, which means we need to figure out what we wan to do before work can start.