[receiver/carbon] Migrate from OpenCensus data model to pdata

[dmitryax]

The receiver still uses OpenCensus data model to create the metrics and converts them into pdata before sending them to the next consumer. This introduces a performance impact. The receiver should use pdata model to create the metrics instead.

[github-actions]

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

[github-actions]

Pinging code owners:

• receiver/carbon: @pjanotti

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[github-actions]

This issue has been inactive for 60 days. It will be closed in 60 days if there is no activity. To ping code owners by adding a component label, see Adding Labels via Comments, or if you are unsure of which component this issue relates to, please ping @open-telemetry/collector-contrib-triagers. If this issue is still relevant, please ping the code owners or leave a comment explaining why it is still relevant. Otherwise, please close it.

Pinging code owners:

• receiver/carbon: @pjanotti

See Adding Labels via Comments if you do not have permissions to add labels yourself.