App/root path improvements

[dcramer]

Let's improve SDKs and how they handle prefixes and app detection.

1. Ensure all SDKs have either include_paths (-1) or project_root, which is used to detect in_app
2. Ensure all SDKs have a list of "prefixes" they can strip. In some cases this can be automatic (Python sys packages, Ruby gems). The project root is automatically included here.

[dcramer]

@getsentry/team if anyone has feedback here

• Python has include_paths and auto strips site-packages
• PHP has "base_path" and "app_path"
• Ruby assumes relative path for app root + some magic

[dcramer]

Also converting PHP to "prefixes" for stripping.

[BYK]

Closing this issue due to staleness. Feel free to comment here if you think we should still work on this.