otlpmetric, otlptrace: interpret compression environment enums case-insensitively #9262

Description

The log exporters interpret compression environment values case-insensitively (#9141, #9133); #9230 lands that by lowercasing the value in convCompression before matching.

The metric and trace exporters still compare exactly, so the shared variable behaves differently depending on the signal. With OTEL_EXPORTER_OTLP_COMPRESSION=GZIP, the log exporters use gzip and the metric and trace exporters silently use no compression.

Four WithEnvCompression implementations parse the value with if v == "gzip":

• exporters/otlp/otlpmetric/otlpmetricgrpc/internal/oconf/envconfig.go
• exporters/otlp/otlpmetric/otlpmetrichttp/internal/oconf/envconfig.go
• exporters/otlp/otlptrace/otlptracegrpc/internal/otlpconfig/envconfig.go
• exporters/otlp/otlptrace/otlptracehttp/internal/otlpconfig/envconfig.go

The specification's environment enum guidance asks for case-insensitive interpretation, which is why #9141 and #9133 were filed for the log exporters.

This issue tracks bringing the metric and trace exporters in line with the log ones, so that a single shared variable resolves the same way for every signal. Work for the individual signals can reference this issue.

Environment

• OS: all
• Architecture: all
• Go Version: all supported
• opentelemetry-go version: main