Update whitepaper

[e-backmark-ericsson]

Changes

Update the CDEvents Whitepaper, copying it from https://cd.foundation/user-stories-and-whitepapers/

Fixes #127

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• [X] Has the primer doc been updated if a design decision is involved
• [X] Have the JSON schemas been updated if the specification changed
• [X] Has spec version and event versions been updated according to the versioning policy
• [X] Meets the CDEvents contributor standards

[e-backmark-ericsson]

@afrittoli , do we need to update https://github.com/cdevents/cdevents.dev/blob/main/content/en/docs/CDEvents_Whitepaper.pdf explicitly as well, or will that be replaced next time we publish the spec to the website?