v1: Add oauth2 support to OTLP output

[philk]

We needed the OTLP configuration to support oauth2 for our specific architecture. I basically copied the configuration from the remote_write side and modified it for the slight differences between the components and it's been working well for us. make build and make test both pass, but I haven't added any test cases for this specifically so that's not surprising.

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[petewall]

Try make build again.