Add sendDefaultPii flag to JS SDK

[Lms24]

The JS SDK currently does not support the sendDefaultPii option that is part of the Sentry SDK specification. We add this option to

1. improve the alignment of the JS SDKs with the other Sentry SDKs
   • This provides an easier way for users to control PII from the SDK
   • and a central flag from which PII relevant data can be controlled for existing features and future development of the SDK
2. be able to control the the dynamic sampling context content w.r.t PII concerns.

Note that full support for the sendDefaultPii flag implies a behaviourally breaking change: We currently instruct users to use hooks like beforeSend, beforeBreadcrumbs or traceSampler to filter out PII on the SDK side. If people do not do this, they will get e.g. user data by default in their events. Since sendDefaultPii defaults to false, users who do not currently filter our PII will not anymore receive this information.

Therefore, we'll introduce this option in two steps:

• Right now, we only add the flag with the intention of controlling dynamic sampling context content
• Implement sendDefaultPii behaviour in the JS SDKs #5347 (tracked in a separate issue. This one is closed once the first step is merged)

[smeubank]

Thanks for creating these @Lms24 !

I would add to point 1. The benefits are also

• to provide an easier way for users to control PII from the SDK
• and a central flag from which PII relevant data can be controlled for existing features and future development of the SDK

Also a note on inspiration:
Organizations can have very different use cases and very different definitions of what is PII. So while the immediate is for DSC. The future of this shall also provide more control and security to organizations that want to control data which might be included in transaction routes or user information for example.