Remove newlines when generating prometheus_endpoint_path

What does this MR do?

Large Prometheus queries are more readable if they are multiline, but we currently do not support multiline Prometheus queries in metrics dashboard yaml files.

The Prometheus query in a metrics dashboard yaml file is passed to the Prometheus server as a GET API query parameter. However, our UrlBlocker does not allow multiline URLs. This prevents us from using multiline Prometheus queries in metrics dashboard.

This MR removes newlines from the Prometheus query before adding it to the API request, thus allowing multiline queries in metrics dashboard yaml files.

Issue: #220338 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

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• Tested in all supported browsers
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Security

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