Unify the terminology of "User Profiles" vs "Attributes"

Notice that right now we use "User Profiles" and "Attributes" changeably. (e.g. look at our doc)

I believe the confusion comes from:

* On Admin Portal or when explain to end users, it is easier to use the term "User Profiles"
* However, in Admin API or user data, we called it `standardAttributes` or `customAttributes`

Assigned it to @fungc-io first, as I believe this issue need some discussion before deciding the next step.

I think it would be better if we:

* Always call it User Profiles, in documentation and in our APIs
* Except when the use case is OIDC, and **\*\*IF OIDC DOES USE THE TERM ATTRIBUTES\*\*,** than we use attributes whenever it is OIDC specific.

Thoughts? @louischan @fungc-io

cc: @pius