Page Impression Instance Amendments

With a review of the data we have consumed, the following amendments have been implemented to increase the relevancy of the data:

- [x] Implement a `page impression id` attribute, to clearly distinguish a single page impression from another
- [x] Rename Flamsteed page impression options to clearly denote the `session id` from the `page impression id`
- [x] Enable `schema` on the Flamsteed page impression instance
- [x] Remove `RUM` calculations on client and send through only raw values
- [x] Ensure `key=value` pairs are correctly populated and sanitized