Please document deprecations

[Guillaume Smet]

Hi,

When rewriting the config to @ConfigMapping, we are stumbling upon quite a lot of deprecated config properties.

Some of them don't have a `since` documenting when the property was deprecated, which forces us to look in the history, which is a bit annoying at scale, especially for external contributors.

Could we make sure that when we add a `@Deprecated`, we mention the since = "3.x" (no need for micro, next minor coming is fine).

Also if we plan to remove this element in the future, let's make sure it has a `forRemoval = true`.

In the case of configuration properties, documenting things in the migration guide is a must and ideally we should add a recipe to rewrite the property when possible. You can find some examples here: https://github.com/search?q=repo%3Aquarkusio%2Fquarkus-updates%20ChangeQuarkusPropertyKey&type=code .

Thanks.

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Guillaume