Add OpenTelemetry attributes to the metrics backend

[adamw]

Currently the OpenTelemetryMetricsBackend reports a number of metrics, following the naming conventions of OpenTelemetry.

However, we only report raw metric values, without any of the attributes as defined here.

The goal of this issue is to report the metrics along with the required attributes. Optionally, we might include other attributes, if this is feasible and "makes sense".

The abstractions currently present in OpenTelemetryMetricsBackend might need updating/extending/refactoring; since this targets version 4 (yet unreleased), there are no compatibility requirements.

[adamw]

/bounty $500

[algora-pbc]

💎 $500 bounty • SoftwareMill

Steps to solve:

1. Start working: Comment /attempt #2292 with your implementation plan
2. Submit work: Create a pull request including /claim #2292 in the PR body to claim the bounty
3. Receive payment: 100% of the bounty is received 2-5 days post-reward. Make sure you are eligible for payouts

Thank you for contributing to softwaremill/sttp!

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Attempt	Started (GMT+0)	Solution
🟢 @varshith257	Oct 16, 2024, 1:10:58 PM	WIP

[varshith257]

@adamw I have experience with OTEL and my experience through an internship and contributions to OTEL and Jaeger. I am throwing my hat to crack this
/attempt #2292

Algora profile	Completed bounties	Tech	Active attempts	Options
@varshith257	16 bounties from 8 projects	Scala, Rust, TypeScript & more		Cancel attempt

[iRevive]

The goal of this issue is to report the metrics along with the required attributes

(copy-paste from softwaremill/tapir#4057).

You can use OpenTelemetry semantic conventions to generate specs and use them in tests to ensure all required attributes are in place.

Here are a few examples:

• semconv-metrics: add MetricSpec, generate tests typelevel/otel4s#773 - metric specs generator in otel4s
• https://github.com/typelevel/otel4s/blob/main/semconv/metrics/stable/src/main/scala/org/typelevel/otel4s/semconv/metrics/HttpMetrics.scala - generated spec
• https://github.com/http4s/http4s-otel4s-middleware/pull/129/files#diff-3f8cb430fb564f7ac7cc04d5658720b1566be69f3dddaac00721f7a69955cb3aR156-R182 - the test itself

[adamw]

@iRevive thanks, this looks interesting. @varshith257 if we could use this somehow to simplify / automate the testing, that would be great

[adamw]

As we are getting first PRs for the bounties, I've published our "How to prepare a good PR" guide. I should have probably done this right away, sorry! :)