#### Description
The last remaining part of #12676 is to implement the `outcome: failure`
part of the Pipeline Component Telemetry RFC ([see
here](https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/rfcs/component-universal-telemetry.md#auto-instrumented-metrics)).
This is done by introducing a `downstream` error wrapper struct, to
distinguish between errors coming from the next component from errors
bubbled from further downstream.
#### Important note
This PR implements things slightly differently from what the text of the
RFC describes.
If a pipeline contains components `A → B` and an error occurs in B, this
PR records:
- `otelcol.component.outcome = failure` in the `otelcol.*.consumed.*`
metric for B
- `otelcol.component.outcome = refused` in the `otelcol.*.produced.*`
metric for A
whereas the RFC would set both `outcome`s to `failure`.
This is programmatically simpler — no need to have different behavior
between the `obsconsumer` around the output of A and the one around the
input of B — but more importantly, I think it is clearer for users as
well: `outcome = failure` only occurs on metrics associated with the
component where the failure actually occurred.
This subtlety wasn't discussed in-depth in #11956 which introduced
`outcome = refused`, so I took the liberty to make this change. If
necessary, I can file another RFC amendment to match, or, if there are
objections, implement the RFC as-is instead.
#### Link to tracking issue
Fixes#12676
#### Testing
I've updated the existing tests in `obsconsumer` to expect a
`downstream`-wrapped error to exit the `obsconsumer` layer. I may add
more tests later.
#### Documentation
None.
---------
Co-authored-by: Alex Boten <223565+codeboten@users.noreply.github.com>
Co-authored-by: Pablo Baeyens <pablo.baeyens@datadoghq.com>
Jade Guiton