Add `otlp_http` for `otlphttp`

[codeboten]

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Describe the issue you're reporting

Depending on the decision in #14099, i'd suggest we add a otlp_http alias for the otlphttp exporter to be consistent with the configuration schema.

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[mbaykara]

I'd like to work on this as well similar to #14099

[andrzej-stencel]

Fixed in #14397