Update documentation for "Keep AltTester Prefab" setting

[andreion1ca]

Overview

This issue tracks the documentation updates required following the implementation of [#188 - Add setting to keep AltTester Prefab if already created in scene].

What needs to be documented

• Describe the new boolean setting introduced to keep the AltTester Prefab in the scene if it has already been manually created
• Explain the purpose of the setting and the problem it solves (avoiding unnecessary recreation of the AltTester Prefab)
• Specify where the setting can be found in the Unity Editor UI
• Document the default value of the setting and the behavior for each state (true / false)

Suggested documentation sections to update

• AltTester Unity SDK — Settings/Configuration reference page
• AltTester Prefab setup guide (if applicable)
• Changelog / Release notes

Screenshots to update

• Update any existing screenshots that show the AltTester settings panel in the Unity Editor to reflect the new boolean setting
• Add new screenshots showcasing the new setting in the Unity Editor UI