feat(asgi): respect suppress_http_instrumentation in ASGI middleware (#4375)

Add is_http_instrumentation_enabled() check in OpenTelemetryMiddleware.__call__
so ASGI server spans are skipped when HTTP instrumentation is suppressed.

Every other HTTP instrumentor (client and server) already honors this flag.
ASGI was the only one that did not.

Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>