Traceability analysis for broken/missing links

[ErikMHP]

Describe the solution you'd like

UbCode should perform full traceability analysis and detect broken or missing references/links for:
• Sphinx-Needs IDs defined in the same project (via .rst)
• Sphinx-Needs IDs imported from external sources (needimport, need_service, etc.)
• Intersphinx references
Errors or warnings shown in the Diagnostics view
Inline highlighting in the .rst file (yellow squiggle) [If possible]

Additional Information
As discussed: The Concern with the Inline highlighting in .rst files is that it could making ubcode very slow, as it needs to update the index while typing/editing.

[ubmarco]

I think we should have configuration to suppress warnings based on:

• target need type
• link type
• target need origin (local, import, external)