Rename `go.opentelemetry.io/contrib/processors/baggage/baggagetrace`

[MrAlias]

• The go.opentelemetry.io/contrib/processors/baggage/baggagetrace package sits on the go.opentelemetry.io/contrib/processors/* prefix. This package prefix will need to be used for log processors as well.
• The baggagetrace package name is not descriptive of the functionality it provides. A name indicating the package provides a SpanProcessor that will copy baggage values into a span should be used instead.

Proposal

1. Copy the package to a new package under the new processors/span directory

• Use processors/span and not processors/trace as this is for a SpanProcessor

2. Rename the package to one of:

• go.opentelemetry.io/contrib/processors/span/bagcp
• go.opentelemetry.io/contrib/processors/span/bagcopy
• go.opentelemetry.io/contrib/processors/span/baggagecp
• go.opentelemetry.io/contrib/processors/span/baggagecopy

3. Deprecate go.opentelemetry.io/contrib/processors/baggage/baggagetrace in favor of the new package.

[dmathieu]

I would go for go.opentelemetry.io/contrib/processors/span/baggagecopy. The long import path shouldn't matter much (and we have longer ones), and it's the clearest name.

[MrAlias]

May not be ideal to split on type. There may be the case where a baggage span processor and log processor are needed.

Instead: go.opentelemetry.io/contrib/processors/baggagecopy and then have NewSpanProcessor and add in the future NewLogProcessor.