Configuration Key For The Open Telemetry Endpoint Is Inconsistent with OpenTelemetry Spec

[sharkymcdongles]

OpenTelemetry spec is here: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/otlp.md

OpenTelemetry Protocol is shortened to OTLP according to their documentation and most libs I have seen.

The config for tracing for cortex however is inconsistent with this and instead uses:

oltp_endpoint

I know this may seem like a Mickey Mouse change, however if you work with opentelemetry extensively you might be in for a bad time when you try to set this like every other implementation.

My proposal is to rename this configuration key to otlp_endpoint for consistency sake.

[sharkymcdongles]

PR here: #5068