Add Practice Exercise: `tree-building`

[0xNeshi]

Problem specification:
https://github.com/exercism/problem-specifications/tree/main/exercises/tree-building

TODO:

• generate the exercise with ./bin/fetch-configlet && ./bin/configlet create --practice-exercise tree-building
• check if any of the existing tracks (examples below) implement the exercise and you can reuse the implementation:
  • Go: https://github.com/exercism/go/tree/main/exercises/practice
  • Rust: https://github.com/exercism/rust/tree/main/exercises/practice
  • Python: https://github.com/exercism/python/tree/main/exercises/practice
• reuse Python's test cases, since there is currently no canonical_data.json:
  https://github.com/exercism/python/blob/main/exercises/practice/tree-building/tree_building_test.py