Create a forked angular preboot with preboot_nonce support

ssr-engine currently uses the angular preboot directly. This is an issue for the following reasons:

- Aurelia isn't in the angular team's scope of work. They could introduce breaking changes.
- PREBOOT_NONCE support for CSP written in their preboot code is only for Angular. There needs to be an Aurelia version.
- Keeping documentation in sync is difficult because changes in angular preboot don't get updated in aurelia's ssr code.

Desired action:

- Fork the project and implement preboot_nonce as part of the work (doesn't look difficult).
- Create a schedule to check for additions/bug fixes in angular preboot. I don't know if there is an existing system for this in Aurelia's workflow system. How are dependencies currently checked for updates in Aurelia?

Start by reviewing how ssr-engine currently uses the Angular preboot dependency, then investigate Aurelia's workflow for checking dependency updates. Done means a maintained fork exists with PREBOOT_NONCE support for Aurelia, along with a documented process for syncing Angular preboot additions and fixes.

Written by the indexing model from the issue text.