[processor/transform] Add initial support for profiles signal

[rockdaboot]

Component(s)

processor/transform

Describe the issue you're reporting

This processor would be useful for testing and validation of the experimental profiling signal.

Adding profiles support to the transformprocessor instead of to the attributesprocessor has been suggested here

[github-actions]

Pinging code owners:

• processor/transform: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley @edmocosta

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[rockdaboot]

I'd like to volunteer.

[mx-psi]

Assigned to you!

[rockdaboot]

On issue that I run to and that needs to be decided is how we want to represent attributes for profiles. For the traditional signals, attributes is a common.Map. In profiles we have AttributeIndices, which is a list of indices pointing into AttributeTable.

For OTTL and the tests in transformprocessor, the following currently doesn't work with profiles:

set(profile.attributes["test"], "pass") where <expr>

-> is not a valid path nor a valid OTTL keyword for the profile context

But letting users deal with attribute indices and attribute table seems like a recipe for havoc.

One possibility would be to have an interface or type pcommon.Attributes with roughly the same methods as pcommon.Map. But I am lacking overall context and there may be more elegant solutions.

[rockdaboot]

Created related issue #39100