feat: support custom metric views in MetricsConfig

[adubovik]

MetricsConfig accepts a new optional meter_provider_views field — a list of opentelemetry.sdk.metrics.view.View — passed straight to the MeterProvider. Previously the only way to customize aggregation was to set the global MeterProvider before init_telemetry ran, which made the SDK's own provider silently lose (Overriding of current MeterProvider is not allowed).

Example — keep the default buckets of http.server.duration but extend them past 10s, up to 5 minutes:

from fastapi import FastAPI
from opentelemetry.sdk.metrics.view import (
    ExplicitBucketHistogramAggregation,
    View,
)

from aidial_sdk.telemetry.init import init_telemetry
from aidial_sdk.telemetry.types import MetricsConfig, TelemetryConfig

app = FastAPI()

init_telemetry(
    app,
    TelemetryConfig(
        metrics=MetricsConfig(
            prometheus_export=True,
            meter_provider_views=[
                View(
                    # NOTE: `http.server.duration` is reported in MILLISECONDS
                    instrument_name="http.server.duration",
                    aggregation=ExplicitBucketHistogramAggregation(
                        # the SDK default boundaries stop at 10s...
                        (
                            0, 5, 10, 25, 50, 75, 100, 250, 500, 750,
                            1000, 2500, 5000, 7500, 10000,
                            # ...these are the extra ones
                            15000, 20000, 30000, 60000, 120000, 300000,
                        )
                    ),
                )
            ],
        )
    ),
)

Scraping :9464/metrics then reports http_server_duration_milliseconds_bucket{...,le="300000"} and friends.

meter_provider_views defaults to None, so existing applications are unaffected.