Improve REST API metrics

[dapplion]

Describe the bug

Only successful requests are registered in metrics. Metrics should register incoming requests, then successful / error requests, and timed out requests

[nflaig]

All metrics besides timeouts are already tracked and we decided that tracking timeouts does not make sense

Errors

lodestar/packages/beacon-node/src/metrics/metrics/lodestar.ts

Lines 221 to 225 in bf5d92b

	errors: register.gauge<"operationId">({
	name: "lodestar_api_rest_errors_total",
	help: "REST API total count of errors by operationId",
	labelNames: ["operationId"],
	}),

Requests total / response times

lodestar/packages/beacon-node/src/metrics/metrics/lodestar.ts

Lines 209 to 220 in bf5d92b

	responseTime: register.histogram<"operationId">({
	name: "lodestar_api_rest_response_time_seconds",
	help: "REST API time to fulfill a request by operationId",
	labelNames: ["operationId"],
	// Request times range between 1ms to 100ms in normal conditions. Can get to 1-5 seconds if overloaded
	buckets: [0.01, 0.1, 1],
	}),
	requests: register.gauge<"operationId">({
	name: "lodestar_api_rest_requests_total",
	help: "REST API total count requests by operationId",
	labelNames: ["operationId"],
	}),