Terms used in User Identity section in CAMARA-API-access-and-user-consent.md

[bhjelm]

Problem description
Update the terms used in User Identity section of CAMARA-API-access-and-user-consent.md

Expected action
The current text isn't clear and mixes the use of (user) "identity," "identification," "identifier" that should be clearly specified in this section (as well as added to the Glossary of Terms section).

Additional context
As suggestion could be to use Section 3.1, 3GPP TR 22.904, as a guide (for User/User Identity/User Identifier) as well as Figure 1, Section 4.2, that depicts the relationship between user, identities, identifiers and attributes. The terminology used also aligns with ISO/IEC 24760 (IT Security and Privacy — A framework for identity management).

[jpengar]

Moving comment from @murthygorty in #93 here, which is a related topic:

In terms and concepts, can you consider changing "User" term to "Subscriber" please? If approved and changed, we will have

End User -> human participant using the application (can be a parent or alternate delegate of the carrier-resource)
Subscriber -> subscriber of the telco operator, owner of the carrier-resource at hand. (eg., parent)

[jpengar]

As stated in #88, we are in the process of finalizing a first release v0.1 of the documentation with the existing agreements. But apart from that, from Telefónica side, we are more than happy if you guys contribute with a PR to the documentation once the v0.1 release is closed, to add the suggested improvement for everyone to review.