feat(vector sink): add multiple endpoint strategies

[fpytloun]

Summary

Adds multi-endpoint support to the vector sink:

• addresses = [...] configures multiple downstream Vector endpoints
• endpoint_strategy = "load_balance" is the default and uses the existing distributed service / endpoint-health path
• endpoint_strategy = "failover" uses ordered, non-preemptive failover for stateful downstream Vector aggregators
• keeps existing address = "..." behavior unchanged
• updates generated component docs and adds a changelog fragment

The failover strategy starts with the first configured endpoint, moves to the next endpoint on request failure or per-endpoint timeout, and keeps using the successful endpoint until it fails. Hosts can use different address ordering to spread primary ownership without requiring random failover semantics.

Validation

• make generate-component-docs
• cargo fmt --all -- --check
• cargo test --no-default-features --features sinks-vector --lib sinks::vector::tests::
• cargo test --no-default-features --features sinks-vector --lib sinks::vector::test::generate_config
• cargo clippy --no-default-features --features sinks-vector --lib -- -D warnings -A clippy::manual_option_zip
• ./scripts/check_changelog_fragments.sh
• Docker Compose E2E:
  • load_balance delivered events to both downstream Vector servers
  • failover delivered only to the first endpoint while healthy, then moved to the second endpoint after the first was stopped with bounded request.timeout_secs

[chatgpt-codex-connector]

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[fpytloun]

Addressed the review comments in the latest push (25ceca6c6f):

• Preserved the old single-address service path so unchanged single-endpoint configs do not go through endpoint-health distributed_service.
• Made ordered failover advance only on retriable Vector errors; non-retriable gRPC statuses such as DataLoss now bubble immediately and are not resent to later endpoints.
• Guarded active endpoint updates so stale concurrent successes cannot preempt a newer failover target.
• Added timeout slack around the internal per-endpoint failover loop so the final endpoint still gets its full per-endpoint timeout budget.
• Added a regression test proving non-retriable primary rejection is not resent to secondary.

Validation rerun:

• cargo fmt --all
• cargo test --no-default-features --features sinks-vector --lib sinks::vector::tests::
• cargo clippy --no-default-features --features sinks-vector --lib -- -D warnings -A clippy::manual_option_zip
• delegated code review: APPROVE

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 25ceca6c6f

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

[fpytloun]

Updated the branch to address the latest review comments:

• Endpoint health now uses the same retriable-error classification as the Vector sink retry logic, so non-retriable Vector responses such as DataLoss do not mark a reachable endpoint unhealthy.
• HealthConfig::default() now matches the documented/serde defaults instead of zero backoff values.
• Failover active-state advancement now uses a generation-aware CAS loop and reloads stale observed state before deciding whether to advance.
• Added focused regressions for health classification, documented health defaults, stale failover generation handling, and stale mismatched-state reload behavior.

Validation:

• cargo fmt --all -- --check
• cargo test --no-default-features --features sinks-vector --lib
• cargo clippy --no-default-features --features sinks-vector --lib -- -D warnings -A clippy::manual_option_zip
• Delegated code review: APPROVE