Integrate prefixes for relative filenames stripping

[kamilogorek]

Reference: https://docs.sentry.io/clients/php/config/
Previous discussion: #670

[mathagician]

@kamilogorek I would like to work on this issue. Since I am new to this, I would seek your help and guidance for this. Please help how to get started.

[kamilogorek]

Hey @mathagician!

Things that need to be done:

• add profixes code to the lib
• add tests covering this change
• update docs

Tests and docs can be based on existing options, which should be (hopefully) readable enough to be reused.

When it comes to code, we need to:

• pass a prefixes option, which will be an array of strings – see prefixes section here https://docs.sentry.io/clients/php/config/
• store it internally as any other option eg. this._globalOptions.prefixes
• write a normalizeUrl, stripPrefixes or something like this function, that'll take a string, check if there are any prefixes, if so, iterate over them and strip anything that has been matched
• apply this function to culprit and all frames from the data payload

Here is a perfect examples where this function should be applied: #634 (comment)

And here's how it's done on for react-native https://github.com/getsentry/react-native-sentry/blob/8b6bea853343d9dfde24735ed55fbf57d5ca2e94/lib/raven-plugin.js#L243-L264

Let me know if you need any more help with it :)

Cheers!