Make otelarrow receiver metrics consistent

[jmacd]

Component(s)

exporter/otelarrow, receiver/otelarrow

Describe the issue you're reporting

The OTel-Arrow project's exporter and receiver are named "otelarrow". The spans and metrics they produce have "otel_arrow" as a substring, and this feels like a consistency problem worth resolving before the components can be marked stable.

Moreover, metrics which are applicable to both OTLP and OTel-Arrow code paths should be made consistent. Presently, the OTLP path does not instrument in-flight bytes, items, and requests.

[github-actions]

Pinging code owners for receiver/otelarrow: @jmacd @moh-osman3. See Adding Labels via Comments if you do not have permissions to add labels yourself.

[github-actions]

Pinging code owners for exporter/otelarrow: @jmacd @moh-osman3 @lquerel. See Adding Labels via Comments if you do not have permissions to add labels yourself.