Update fts information according to not indexed design-time roles

[lovtsovaik]

Environment

Documentation version: 7.2
Part of the documentation: FTS
Existing page: https://doc.cuba-platform.com/fts-7.2/fts.html

Description of the bug or enhancement

Design-time roles are not indexed (see cuba-platform/fts#77)
Therefore:

• Figure 4. "Search Results" is not actual (see also issue Update fts example according to a new set of roles #758)
• Not actual information is in the last sentence of paragraph 3.3:

full-text search should work for all entities of the application model as well as entities of the framework security subsystem: Role, Group, User.

It is necessary to update information according to a new behavior: search by design-time roles will give no result.