Further alignment of CAMARA-API-access-and-user-consent.md with API consumer and API provider terms

[jpengar]

Problem description

Update CAMARA-API-access-and-user-consent.md to achieve further alignment in the use of the terms "API Consumer" and "API Provider" (replacing other potential synonyms used) and to avoid the term "Telco" which has been reported in the past. These changes will be only naming/wording changes and no technical information in the specification document is changed.

For example:

• Replace "API Invoker" with "API Consumer".
• Remove mentions of the term "Telco".

Expected action

Create a new PR just to update these terms, with no further changes beyond the original scope of the issue.

Additional context

N/A