Document OTEL_EXPORTER_OTLP_[LOGS|TRACE|METRICS]_INSECURE and OTEL_EXPORTER_OTLP_INSECURE env vars in OTLP HTTP/protobuf exporters

[pellared]

See: #7608

Moreover,

Note that otlpmetrichttp and otlptracehttp also do not support such env vars.

This doesn't seem to be the case

opentelemetry-go/exporters/otlp/otlpmetric/otlpmetrichttp/internal/oconf/envconfig.go

Lines 92 to 93 in dafdbf8

	envconfig.WithBool("INSECURE", func(b bool) { opts = append(opts, withInsecure(b)) }),
	envconfig.WithBool("METRICS_INSECURE", func(b bool) { opts = append(opts, withInsecure(b)) }),

opentelemetry-go/exporters/otlp/otlptrace/otlptracehttp/internal/otlpconfig/envconfig.go

Lines 91 to 92 in dafdbf8

	envconfig.WithBool("INSECURE", func(b bool) { opts = append(opts, withInsecure(b)) }),
	envconfig.WithBool("TRACES_INSECURE", func(b bool) { opts = append(opts, withInsecure(b)) }),

So at least the Go impl is also not in compliance with the spec and is internally inconsistent.

Originally posted by @fd in #7608 (comment)

[pellared]

So at least the Go impl is also not in compliance with the spec and is internally inconsistent.

Thanks, we would need to double-check (I think you are correct). At least it is not documented (therefore, not officially supported) in https://pkg.go.dev/go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp and https://pkg.go.dev/go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp.

@open-telemetry/go-maintainers, any opinions what we should do? I see the following options

1. Leave as it is (undocumented feature that is not officially supported)
2. Add to the spec and document
3. Remove the support for these env vars

[MrAlias]

SIG notes:

• moratorium on envar in the spec is probably why this doesn't exist there
• we should just do the right thing for our users and add the envar support to logs if we already do so for traces and metrics

[pellared]

Updated the title as #7608 is merged. Now, we just need to update the packages documentation.