feat(question): add #15260 - Tree path array (#15261)

Co-authored-by: Neil Richter <19751938+noook@users.noreply.github.com>

questions/15260-hard-tree-path-array/README.md

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+Create a type `Path` that represents validates a possible path of a tree under the form of an array.
+
+Related challenges:
+- [Object key path](https://github.com/type-challenges/type-challenges/blob/main/questions/07258-hard-object-key-paths/README.md)
+
+```ts
+declare const example: {
+    foo: {
+        bar: {
+            a: string;
+        };
+        baz: {
+            b: number
+            c: number
+        }
+    };
+}
+
+/* Possible solutions: 
+[]
+['foo']
+['foo', 'bar']
+['foo', 'bar', 'a']
+['foo', 'baz']
+['foo', 'baz', 'b']
+['foo', 'baz', 'c']
+*/
+```

questions/15260-hard-tree-path-array/info.yml

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+difficulty: hard
+title: Tree path array
+author:
+  github: noook
+  name: Neil Richter
+

questions/15260-hard-tree-path-array/template.ts

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+type Path<T> = any

questions/15260-hard-tree-path-array/test-cases.ts

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+import type { ExpectTrue,ExpectFalse,ExpectExtends } from '@type-challenges/utils'
+
+declare const example: {
+    foo: {
+        bar: {
+            a: string;
+        };
+        baz: {
+            b: number
+            c: number
+        }
+    };
+}
+
+type cases = [
+  ExpectTrue<ExpectExtends<Path<typeof example['foo']['bar']>, ['a']>>,
+  ExpectTrue<ExpectExtends<Path<typeof example['foo']['baz']>,['b'] | ['c'] >>,
+  ExpectTrue<ExpectExtends<Path<typeof example['foo']>, ['bar'] | ['baz'] | ['bar', 'a'] | ['baz', 'b'] | ['baz', 'c']>>,
+  ExpectFalse<ExpectExtends<Path<typeof example['foo']['bar']>, ['z']>>,
+]