Restrict GET /users API to authenticated users

[isabelcosta]

Description

• This PR restricts the GET /users API for authenticated users.
• This should be merged after PR Integrate flask-jwt-extended #64 which fixes some exception throwing from flask-jwt library.
• Restrict some information of users, that should not be seen by other users. (needs discussion)
  • Username -> visible
• Make GET /users/verified also retricted

Fixes #72

Type of Change:

• Code

Code/Quality Assurance Only

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Tested GET /users API on Swagger UI
• Developed a test to attempt to access this API without an access token

Checklist:

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials
• Any dependent changes have been merged
• Update Swagger documentation and the exported file at /docs folder

Code/Quality Assurance Only

• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[isabelcosta]

@m-murad @Dilu9218 until we add environment variables for the email verification on the deployed server, its best if we don't merge this, to better debug if a user is being registered into the system. To be able to check the users list without being logged in

[Dilu9218]

please solve conflicts in the same swagger.json :)

[isabelcosta]

@Dilu9218 conflicts are fixed!