Basic fields in the transaction context are missing and are not settable

[zobo]

Is your feature request related to a problem? Please describe.
I am missing basic information like REMOTE ADDRESS, COOKIES and there is no API to set these.
For example:
https://github.com/elastic/apm-server/blob/52be7fe64897131117148fa9f5e4b7757c76814f/docs/spec/request.json#L45
https://github.com/elastic/apm-server/blob/52be7fe64897131117148fa9f5e4b7757c76814f/docs/spec/request.json#L96
https://github.com/elastic/apm-server/blob/52be7fe64897131117148fa9f5e4b7757c76814f/docs/spec/request.json#L11

Describe the solution you'd like
I want to be able to configure or set these values myself.

Describe alternatives you've considered
I have researched the source and was not able to find a way to set these, without modifying the PHP agent implementation.