MAB-741: Limit permissions to add roles to user

[Joselgc1]

Description

The bug was that users could still see wrong role options in the UI. It is now fixed by filtering assignable roles server-side based on can_see_users and can_add_users., passing preview role context correctly, and updating user edit/invite screens to use that filtered list. Also hid the Groups section when it has no usable options.

Useful links

• https://www.notion.so/Limit-permissions-to-add-roles-to-user-314d463fd8c480899102c07160f11727?source=copy_link

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (refactor or addition to existing functionality)

Checklist:

( * == Mandatory )

• * I have set myself as assignee of the pull request
• * My code follows the style guidelines of this project
• * Linting does not generate new warnings
• * I have performed a self-review of my own code
• * I have put the ticket for review, adding the oort-frontend team to the list of reviewers
• * I have commented my code, particularly in hard-to-understand areas
• * I have put JSDoc comment in all required places
• * My changes generate no new warnings
• * I have included screenshots describing my changes if relevant
• * I have selected labels in the Pull Request, according to the changes with code brings
• I have made corresponding changes to the documentation ( if required )
• 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
• Any dependent changes have been merged and published in downstream modules