[receiver/signalfx][exporter/signalfx] Accept otlp metrics in signalfx receiver/exporter

[jinja2]

Component(s)

receiver/signalfx
exporter/signalfx

Describe the issue you're reporting

Update the signalfx receiver to accept otlp metrics when incoming requests have the header set to application/x-protobuf;format=otlp
Update signalfx exporter to send otlp

[crobert-1]

/label enhancement -needs-triage

[github-actions]

Pinging code owners for receiver/signalfx: @dmitryax. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[sakulali]

Hello @crobert-1, could you please assign this issue to me, i would like to spend some time resolving this feature, thanks

[atoulme]

Thanks for your initial contribution! We deeply appreciate it. However, @jinja2 is working on a design behind this change and will make more design changes based on requirements. For now, reassigning the issue to @jinja2 as she is writing things down.