fix: use release-health flag in sentry-actix and remove it from subcrates where unneeded

[lcian]

Removes the release-health feature from sentry-tower and sentry-tracing, where it was used unnecessarily.

It's still a feature flag, enabled by default, in sentry-actix, as it's used there to create a session per request.
This was the default behavior previously, with no way of opting out, so it makes sense to keep it enabled by default there.

sentry-rust/sentry-actix/Cargo.toml

Line 16 in 3cc461a

default = ["release-health"]

I've fixed it to actually be used in the code because compilation would fail otherwise due to the hub.start_session(); call.

There is no change to the sentry crate, where this flag is part of the default features as intended:

sentry-rust/sentry/Cargo.toml

Line 30 in 3cc461a

"release-health",

Note that sentry has no way to bring in sentry-actix via feature flags.
Is there a reason for that?
I'll create a separate PR to enable it, similarly to other integrations.

[Swatinem]

you should probably move the #[cfg] up to where you define this field. I believe the client options auto_session_tracking is also not available with this feature, right?

[lcian]

At the moment the option is available even without the flag, I've just added a doc line on it to make it clear that the feature flag needs to be enabled for that option to have any effect.

But, I think both auto_session_tracking and session_mode in ClientOptions should instead not be available if the feature is not enabled.
This way, if someone uses those options but their deps don't bring in sentry-core/release-health, it will fail to compile. Better than no-opping silently.

I will update the PR.

[lcian]

Now it should be good.

[Swatinem]

I think we are still running this test in CI, are we?

[lcian]

Actually the whole session.rs is wrapped in:

#[cfg(feature = "release-health")]
mod session_impl {

So effectively these extra cfg macros inside it are useless. Removed them.