feat: Generate more telemetry via TelemetryAPI receiver

[borchero]

Motivation

The current implementation of the Telemetry API receiver only generates init spans. However, it can easily be extended to create

• spans for the entire function invocation
• metrics for function invocations

This PR leverages the events provided by the Telemetry API to implement the latest semantic conventions for FaaS spans and metrics.

It also updates the coldstartprocessor to become a more general faasprocessor.

Please read through the READMEs of the telemetryapnireceiver and the faasprocessor for an overview of the changes.

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I did not yet write unit tests (and only checked functionality manually) but wanted to check with the maintainers first whether this change would be desirable to include into this project.

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This PR supersedes #1216.

[tylerbenson]

@rapphil I'm curious what you think about this.

[tylerbenson]

@borchero Do you have interest in finishing this out or should we close the PR? I think it's a promising improvement.

[gkaskonas]

Any plans to finish this?

[github-actions[bot]]

Closed as inactive. Feel free to reopen if this PR is still being worked on.