add metric for total number of requests

[xinau]

currently only response errors are counted, while this it self is useful it would be more complete to also log the total number of requests. by comparing the ratio of errors and total requests a operator is able to determine the healthiness of their installations.

the concrete change needs to be made somewhere along these lines. i'm still unsure how to implement it "correctly", but would like to contribute to the project. 2 solutions that come to my mind would be to either.

1. drop the if clause and count all responses
2. add a new metric keycloak_responses_total similar to keycloak_response_errors that counts all responses

keycloak-metrics-spi/src/main/java/org/jboss/aerogear/keycloak/metrics/MetricsFilter.java

Lines 44 to 48 in a9ede42

	// We are only interested in recording the response status if it was an error
	// (either a 4xx or 5xx). No point in counting the successful responses
	if (status >= 400) {
	PrometheusExporter.instance().recordResponseError(status, req.getMethod());
	}

[pb82]

@xinau That sounds reasonable. But if the goal is assessing the health, wouldn't a rate on the response errors also do the job?

[xinau]

@pb82 Using the error rate can be misleading. I.x. I do know when there is a larger response errors than expected, but this could also be the case when the overall traffic went up and shouldn't need to worry me in the case the error to total response ratio remains the same.

If it's okay with you I can provide a timely patch and tests.