fix: query string included for the first collapsed path segment

[mehdimas]

When the first path segment of a request has a query string the metrics middleware includes the query string in a collapsed path.

For example, /hello?uid=46cfcbdd-fd45-4fb2-a301-47bc24024b5c produces a metric like this:

ory_oathkeeper_requests_total{method="GET",request="hello?uid=46cfcbdd-fd45-4fb2-a301-47bc24024b5c",service="test",status_code="200"} 1

If the query string contains non-static values, then a new prometheus metric will be created for each request. The number of metrics increasing over time could cause stability issues.

The expected metrics should be a collapsed path like:

ory_oathkeeper_requests_total{method="GET",request="hello",service="test",status_code="200"} 1

This PR truncates any query string when collapsing the path.

Related issue(s)

Original metrics cardinality issue: #446

Checklist

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  introduces a new feature.
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• I have added tests that prove my fix is effective or that my feature
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Further Comments

The results of this issue are also visible in standard Oathkeeper Grafana dashboard:

[CLAassistant]

All committers have signed the CLA.

[aeneasr]

Awesome, thank you!