Add OpenTelemetry Proto Metrics Reader Extension

[suraj-goel]

Fixes #17644.

Description

• Added OpenTelemetry Proto Metrics Reader extension.
• Benchmark results

Release note

• A new extension, druid-opentelemetry-extensions, has been added to enable ingestion of metrics in OpenTelemetry Protocol (OTLP) format.
• This extension allows Druid to ingest metrics data directly from OpenTelemetry sources using the OTLP format, aligning Druid with industry-standard telemetry protocols.
• To use this extension, refer to attached README

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[FrankChen021]

We already an extensions named as opentelemetry-emitter which supports emitting tracing logs, and the new extension in this PR is druid-opentelemetry-extensions, which looks like an extensions that includes the emitter. I'm worried that this might cause some confusion.

Since the extension supports ingestion data in the opentelemetry proto format, maybe we can rename it as `druid-opentelemetry-metric-extensions' or sth else.

[suraj-goel]

We already an extensions named as opentelemetry-emitter which supports emitting tracing logs, and the new extension in this PR is druid-opentelemetry-extensions, which looks like an extensions that includes the emitter. I'm worried that this might cause some confusion.

Since the extension supports ingestion data in the opentelemetry proto format, maybe we can rename it as `druid-opentelemetry-metric-extensions' or sth else.

Right now, this extension supports ingestion of protobuf OTLP Metrics events.
The idea is that we can extend the same extension further to include OTLP traces and spans.

Let me know if this makes sense.

[FrankChen021]

From the general software design principle, it makes sense to leave a room to add trace and span logs in future.

However, from reality, I would like to argue that if Druid is the right choice for span logs. For span logs, scan queries or point queries are mainly involved, and because Druid lacks rerverted index, bloom filter index, serving these needs would not be a good idea. And now, i also don't see Druid has any plan on the the index or storage layer to support these scenarios.

[suraj-goel]

@FrankChen021, As per your suggestion, I have renamed the extension.