add a feature to the metricstransformprocessor to allow custom code to do the transformation

[preetmyob]

Component(s)

https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/processor/metricstransformprocessor

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

Use case:

we have an old (non-oTel) custom metrics collector that transforms metrics by running some custom code to perform some custom renaming/modification of metrics.

Notes:

This is an obscure activity so this particular transform would never likely be used by other people, so not likely to be a candidate for the control project. However, being able to make your transforms would potentially enable more people to move from legacy collection schemes to oTel.

Caveats

How to support:

• multiple languages
• multiple platforms

Perhaps picking a single cross-platform language would be sufficient.

Describe the solution you'd like

A new processor with the ability to run some custom code, package, and follow a well-defined interface. With the defined input of the metric, and the defined output of the transformed metric.

Describe alternatives you've considered

1. Just writing an entire processor that would likely just be used by us. This would have the added maintenance of keeping it synced with the project changes.

2. Writing finding a way to add attributes to the transformation chain that an existing transformer can use (perhaps the regexp one)

Additional context

No response