* web: replace deprecated InstrumentHandler()
This change replaces the deprecated InstrumentHandler function by the
equivalent functions from the promhttp package.
The following metrics are removed:
* http_request_duration_microseconds (Summary).
* http_request_size_bytes (Summary).
* http_requests_total (Counter).
And the following metrics are added instead:
* prometheus_http_request_duration_seconds (Histogram).
* prometheus_http_response_size_bytes (Histogram).
* promhttp_metric_handler_requests_in_flight (Gauge).
* promhttp_metric_handler_requests_total (Counter).
* Update github.com/prometheus/common/route package
* web: refactor using the new prometheus/common/route package
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