Remove expandconverter

[bogdandrutu]

Need to investigate if the current expand providers logic in the confmap.Resolver has all the equivalent functionality. Then we also need to propose some kind of deprecation process: e.g. disable by default via a featuregate; or other alternatives.

One caveat that I know and need to document is that because of this we have a workaround in prometheus receiver see the note here. Once this is disable that is no longer necessary which is a good thing, but may break some users so we need to find a way to handle/communicate that.

[mx-psi]

but may break some users so we need to find a way to handle/communicate that.

We may want to have some sort of subcommand/flag/separate tool to migrate a config from the old syntax to the new one. This could be useful for other future changes in the configuration (whether breaking or just recommendations). If that sounds like a good idea, should we create a separate issue to discuss how to go about it?

[bogdandrutu]

Let's start that issue. We definitely need it. I think the best we can do is to have it as a subcommand but this is just me prematurely commenting 👯

[mx-psi]

See #7631 :)

[mx-psi]

Per #8215 (comment) before doing this we need to add support for ${...} to the general expansion before removing this converter, to align with open-telemetry/opentelemetry-specification#3744