Refactor tail-sampling processor - Move to OTel metrics instead of OpenCensus metrics

[jpkrohling]

[github-actions]

Pinging code owners for processor/tailsampling: @jpkrohling. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[github-actions]

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Pinging code owners:

• processor/tailsampling: @jpkrohling

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

[codeboten]

Related to #29867