feat(vector sink): Add connection_ttl_secs config for load balancing

[Shell32-Natsu]

Summary

This PR adds a connection_ttl_secs configuration option to the vector sink that allows connections to be periodically closed and re-established. This addresses load balancing issues where long-lived HTTP/2 connections prevent proper distribution of traffic across backend instances.

When connection_ttl_secs is set, the sink will track the age of each connection and automatically recreate the underlying HTTP/2 client after the specified duration. This forces a reconnection through the load balancer, allowing traffic to be distributed to different backend instances.

Vector configuration

[sinks.my_vector_sink]
type = "vector"
address = "http://load-balancer:6000"
compression = true
connection_ttl_secs = 300  # Reconnect every 5 minutes

Without the option (default behavior - unlimited connection reuse):

[sinks.my_vector_sink]
type = "vector"
address = "http://load-balancer:6000"

How did you test this PR?

1. Unit tests: Added test_connection_ttl_config to verify configuration parsing with and without the TTL option
2. Build verification: Confirmed the implementation compiles successfully with cargo build --package vector --lib --features "sinks-vector"
3. Test suite: All existing vector sink tests pass

The implementation tracks connection creation time and checks before each request whether the TTL has been exceeded. When expired, it recreates the hyper HTTP/2 client and gRPC client transparently.

Change Type

[ ] Bug fix
[x] New feature
[ ] Non-functional (chore, refactoring, docs)
[ ] Performance

Is this a breaking change?

[ ]Yes
[x] No

Does this PR include user facing changes?

[x] Yes. Please add a changelog fragment based on our guidelines.
[ ] No. A maintainer will apply the no-changelog label to this PR.

References

This addresses the common issue where HTTP/2 connection multiplexing and keep-alive prevent load balancers from distributing traffic across multiple backend instances, as HTTP/2 connections are designed to be long-lived and reused.

[pront]

Hi @Shell32-Natsu, can you add a changelog fragment since this is a user facing change? Thanks!

[Shell32-Natsu]

Will do!

[Shell32-Natsu]

Added

[Shell32-Natsu]

Hi @pront Could you take a look? Thanks!

[pront]

Suggested change

	pub(in crate::sinks::vector) connection_ttl_secs: Option<u64>,
	pub connection_ttl_secs: Option<u64>,

[pront]

One question for my understanding: What happens to active requests if TTL expires?

[pront]

This silently ignores errors when rebuilding the proxy connector. If client recreation fails, it continues with the old client without logging or alerting.

Also, worth considering emitting internal metrics tracking recreations.

[pront]

We can at least add self.client.created_at here but also can we just derive debug here? Is it too verbose?