Add documentation for core OpenAthena engine components

[mkrupczak3]

Currently, the GitHub page only provides limited documentation for developers.

UML diagrams and markdown documentation should be created for the following engine components:

• Drone image metadata parsing in MetadataExtractor.java
• Camera intrinsics modeling in MetadataExtractor.java
• DEM parsing in DEMParser.java
• Singleton finite state machine for engine management in AthenaApp.java
• Terrain-Raycast simulation in TargetGetter.java