feat(cdp): add pii hashing transformation

[meikelmosby]

Problem

we want a way to hash PII through transformations, also on nested values e.g. properties.$ip or properties.$set.$email

Changes

• introduced new transformation that can hash any field in properties.
• we handle nested properties as well e.g. properties.$set.$default_browser
• you also hash the distinct_id
• you can optionally provide a salt

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Does this work well for both Cloud and self-hosted?

How did you test this code?

• written tests
• tested locally

[greptile-apps]

PR Summary

Introduced a new PII data hashing transformation that uses SHA-256 to protect sensitive user data in event properties, with configurable property selection.

• Implemented SHA-256 hashing in /plugin-server/src/cdp/templates/_transformations/pii-hashing/pii-hashing.template.ts with default IP address hashing
• Added comprehensive test suite in pii-hashing.template.test.ts covering edge cases like empty values and invalid paths
• Template preserves original event structure by creating a copy before modification
• Includes input schema for flexible property selection via dictionary configuration
• Maintains data integrity by only hashing non-empty values and leaving unspecified properties unchanged

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