WPF 886828 - Updated Gantt UG content changes

[TamilarasanGunasekaran]

I have updated Gantt UG content changes and API links for all files.

[SyncfusionBuild]

Build Status: INQUEUE 🕒
Build Location: Gantt_content_changes

[SyncfusionBuild]

Build Status: INPROGRESS 🔃
Build Location: Gantt_content_changes

[SyncfusionBuild]

CI Status: FAILURE ❌
Source Compilation: SUCCESS ✅
Failure Reason: CI Failure with violation
Build Location: Gantt_content_changes
Image Alt Text Error(s): 0
Image Size Error(s): 1
Image Name Error(s): 0
FT Layout Syntax Error(s): 0
Front matter Error(s): 0
File Path Error(s): 0
CodeSnippet File Path Missing Error(s): 0
Toc Anchor Tags Validation Error(s): 0

[SyncfusionBuild]

Build Status: INPROGRESS 🔃
Build Location: Gantt_content_changes

[SyncfusionBuild]

CI Status: SUCCESS ✅
Source Compilation: SUCCESS ✅
Build Location: Gantt_content_changes
Image Alt Text Error(s): 0
Image Size Error(s): 0
Image Name Error(s): 0
FT Layout Syntax Error(s): 0
Front matter Error(s): 0
File Path Error(s): 0
CodeSnippet File Path Missing Error(s): 0
Toc Anchor Tags Validation Error(s): 0