[Trust Domains] Align documentation with CAMARA actors and terms

[caubut-charter]

Problem description
Not aligned with CAMARA.

Expected action
Audit the repo and align with CAMARA.

Additional context
Examples to look out for:

• API Consumer in place of other labels representing the third-party API client.
• API Provider in place other labels like Network Operator.

[caubut-charter]

Make sure to remove CPE. Closing #14.