Update SAMM to AAS mapping documentation for AAS v3 (#619)

[gjavakhadze]

Description

Updates java-aas-mapping.adoc to align the documentation with the current AAS v3 generator implementation (core/esmf-aspect-model-aas-generator). Also added explanation why some statements are in bold style and rest of them not.

Fixes #619

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works