Add allowUrls as a config option for web instrumentation

[jairo-mendoza]

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NB: Before opening a feature request against this repo, consider whether the feature should/could be implemented in the other OpenTelemetry client libraries. If so, please open an issue on opentelemetry-specification first.

Is your feature request related to a problem? Please describe.

Not a problem, but more of a nice to have that could help with handling restrictions without having to disallow specific urls explicitly.

Describe the solution you'd like

A config option holding an array of urls or a regex for both the FetchInstrumentation and XMLHttpRequestInstrumentation classes. Requests will then be checked against allowUrls, not sending a span if there isn’t a match. Similar solution can be implemented for DocumentLoadInstrumentation over on the contrib repo.