fix: query string included for the first collapsed path segment

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: https://github.com/ory/oathkeeper/issues/446

Checklist

[x] I have read the contributing guidelines.
[x] I have referenced an issue containing the design document if my change introduces a new feature.
[x] I am following the contributing code guidelines.
[x] I have read the security policy.
[x] I confirm that this pull request does not address a security vulnerability. If this pull request addresses a security vulnerability, I confirm that I got the approval (please contact security@ory.sh) from the maintainers to push the changes.
[x] I have added tests that prove my fix is effective or that my feature works.
[x] I have added or changed the documentation.

Further Comments

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

ory / oathkeeper