Create placeholders for Internal Event Tracking documentation

What does this MR do and why?

This MR links to issue #414543 (closed)

The goal of this MR is to create placeholders for documentation around Internal Event Tracking.

Update 6 files

• /doc/development/internal_analytics/index.md
• /doc/development/internal_analytics/internal_event_tracking/introduction/index.md
• /doc/development/internal_analytics/internal_event_tracking/quick_start/index.md
• /doc/development/internal_analytics/internal_event_tracking/event_definition_guide/index.md
• /doc/development/internal_analytics/internal_event_tracking/architecture/index.md
• /doc/development/internal_analytics/internal_event_tracking/index.md

MR acceptance checklist

• I have evaluated the MR acceptance checklist for this MR.
• Reviewed by all reviewers
• All Engineers are aware of the placeholders. Engineers, please check mark against your name to acknowledge
  • @bastirehm
  • @ankit.panchal
  • @pskorupa
  • @j_lar
  • @michold
  • @nbelokolodov
• Navigation is updated