NC | IAM | Docs | Update Terminology Part

[shirady]

Explain the changes

1. Update the terminology in IAM docs to make the terms easier to understand.

Issues:

List of GAPs:
The docs were written under the assumption:

1. The structure with users/ directory (one of the following PR after NC | Config Dir Restructure #8279 that was not published yet).
2. A fix to the gap that an IAM user can create a bucket using the S3API (as mentioned in PR NSFS | NC | IAM Service - Accounts Permission When No Bucket Policy #8175).

Testing Instructions:

1. none

• Doc added/updated
• Tests added