feat(pipeline): support Loki API

[shuiyisong]

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Refer to a related PR or issue link (optional)

close #4800

What's changed and what's your intention?

This PR adds support for the Loki API to run pipelines.
The process becomes a little complicated; see the diagram below for a quick glimpse.

For entering the pipeline process

1. The original ts (in nanosecond timestamp datatype), Loki text line, and all the labels and structure metadata are merged into one big map
2. This map is used as the input data of the pipeline

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[Copilot]

Pull Request Overview

Adds support for running pipelines on incoming Loki payloads by routing HTTP ingest through the pipeline engine when a pipeline header is present, introducing iterator-based JSON/Protobuf parsers, and validating functionality with new integration tests.

• Route loki_ingest through run_pipeline when GREPTIME_PIPELINE_NAME_HEADER_NAME is provided.
• Implement LokiJsonParser/LokiPbParser and extract_item to convert streams into generic item iterators.
• Include new integration tests (test_loki_pb_logs_with_pipeline, test_loki_json_logs_with_pipeline) for the pipeline path.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests-integration/tests/http.rs	Added two integration tests covering PB and JSON payloads with pipeline execution.
src/servers/src/http/loki.rs	Refactored ingest handler to support optional pipeline, extracted parsing logic into dedicated parsers and iterator adapters.
src/pipeline/src/lib.rs	Exported Timestamp in the public API and removed now-unused unwrap_or_warn_continue macro.

Comments suppressed due to low confidence (3)

src/pipeline/src/lib.rs:52

• The unwrap_or_warn_continue macro has been removed; ensure no downstream code references it or update consumers accordingly.

}

tests-integration/tests/http.rs:3962

• [nitpick] Consider adding negative or malformed-payload tests (e.g., invalid pipeline name or bad YAML) to cover failure paths for the pipeline ingest logic.

pub async fn test_loki_pb_logs_with_pipeline(store_type: StorageType) {

src/servers/src/http/loki.rs:55

• [nitpick] Verify that use crate::pipeline::run_pipeline points to the intended module and consider unifying imports (e.g., consistently using either pipeline::run_pipeline or crate::pipeline::run_pipeline) for clarity.

use crate::pipeline::run_pipeline;

[killme2008]

LGTM