NH-70998 OTLP response_time metrics in milliseconds

[tammy-baylis-swi]

Fixes OTLP response_time metrics so they're reported in milliseconds (not nanoseconds, as before).

Here is a test otelcol metrics message following a request to a route with a time.sleep(3) included:

Metric #0
Descriptor:
     -> Name: trace.service.response_time
     -> Description: measures the duration of an inbound HTTP request
     -> Unit: ms
     -> DataType: Histogram
     -> AggregationTemporality: Cumulative
HistogramDataPoints #0
Data point attributes:
     -> sw.is_error: Str(false)
     -> http.status_code: Int(200)
     -> http.method: Str(GET)
     -> sw.transaction: Str(unused)
StartTimestamp: 2024-02-01 18:28:18.418123297 +0000 UTC
Timestamp: 2024-02-01 18:28:18.420461838 +0000 UTC
Count: 1
Sum: 3017.000000
Min: 3017.000000
Max: 3017.000000

[cheempz]

LGTM @tammy-baylis-swi pending one question.