Should support custom metrics prefix

[zwpaper]

Description

ogen now use a const metrics key:

ogen/otelogen/keys.go

Line 38 in e147d5e

ServerRequestCount = "ogen.server.request_count" // Incoming request count total

but maybe provide a way to set a prefix would be great for users, resulting something like:

<PROJECT>_duration_milliseconds_count{otel_scope_name="github.com/ogen-go/ogen",otel_scope_version="semver:0.2.0"} 2
# HELP <PROJECT>_request_count_total Incoming request count total
# TYPE <PROJECT>_request_count_total counter
<PROJECT>_request_count_total{otel_scope_name="github.com/ogen-go/ogen",otel_scope_version="semver:0.2.0"} 2

References