[receiver/collectd] 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:

• receiver/collectd: @atoulme

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[github-actions]

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

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Pinging code owners:

• receiver/collectd: @atoulme

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[ZenoCC-Peng]

I would like to work on this!

[ZenoCC-Peng]

Hi, @atoulme, @dmitryax

I am simply curious about the time.
Currently, I have made some modifications to the code.

The initial implementation of time utilizes the metricspb library, where timestamps are represented as numerical values denoting seconds and nanoseconds.

For example, in the collectd_test.go,

*metricspb.Point{ { Timestamp: &timestamppb.Timestamp{ Seconds: 1415062577, Nanos: 496000000, }, Value: &metricspb.Point_DoubleValue{DoubleValue: 0.2}, } .

However, the pdata version, when we use SetTimestamp to assign timestamps for a datapoint, adopts the UTC time zone format, such as "2014-11-04 00:56:17.496 +0000 UTC,". Although we can covert UTC time zone to numerical values, I am curious whether it is feasible to modify the code to utilize SetTimestamp with UTC time zone. If it is possible, I believe we should include a note in our documentation.