Adding Gen 6 Ambush Encounters

[ItsMeJoji]

Change description

This PR consists of the X and Y Ambush encounters that were missing.

This includes additions of new Encounters, Encounter Methods, and Encounter Conditions.

This would close Issue #1454.

AI coding assistance disclosure

No AI was used in adding these.

Contributor check list

• I have written a description of the contribution and explained its motivation.
• I have written tests for my code changes (if applicable).
• I have read and understood the AI Assisted Contribution guidelines.
• I will own this change in production, and I am prepared to fix any bugs caused by my code change.