[telemetrygen] Support metrics delta temporality

[ArthurSens]

Component(s)

cmd/telemetrygen

Is your feature request related to a problem? Please describe.

We're starting to work on supporting OTLP deltas in Prometheus' OTLP endpoint and it would be awesome if telemetrygen could generate metrics with that temporality to help us with tests :)

Describe the solution you'd like

an extra flag in telemetrygen that changes the metric temporality

Describe alternatives you've considered

We could find a component that generates some random deltas, it's not as well-controlled though

Additional context

No response

[github-actions]

Pinging code owners:

• cmd/telemetrygen: @mx-psi @codeboten @Erog38

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[mx-psi]

I think this would be a great addition

[NickAnge]

Hey everyone, I would like to work on this if that is ok. It would be my first issue with the collector

[ArthurSens]

Absolutely :) Feel free to ping if you need help

[NickAnge]

Hello @mx-psi . I raised this PR to tackle the support of delta temporality by adding a simple cli flag temporality-type

However I am not sure if I need to change something related with the StartTimestamp and Timestamp. Based on the documentation, I understand the difference between cumulative and delta. However its not clear (or I missed it) if this is something that will be handled by the metrics generator (telemetrygen) or the respective observability backend.

Cumulative implementation (Without the delta addition)

With the current implementation, I see that the StartTimestamp is different for each datapoint that is generated. code, so my assumption is that is handled by the backend and we just need to set the Aggregation Temporality

OR the usage of the i is actually the cumulative behaviour by increasing it by one each time that we push the datapoint. So basically the telemetrygen "stores" the value for the period that it generates, but again it doesn't use the StartTimestamp properly. I mean based on the doc 🤔

Could you please clarify this if you know ? Thanks in advance

[mx-psi]

I think the current cumulative points are, while technically valid, not very useful. I see that as a bug on telemetrygen that we can fix, but we can probably do this independently of the feature you want to add. The approach on the PR you sent looks okay to me, I am happy to give more detailed feedback once you mark as ready for review