Create mentoring.md

tracks/typescript/exercises/etl/etl/mentoring.md

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+# Mentoring
+
+## ETL
+
+### Problem asks
+Restructure grouped letters by point values into individual mappings. 
+Transform the old format (point-value groups) 
+into a new format (letter-score pairs) in TypeScript. 
+Associate lowercase letters with their corresponding point values, 
+transitioning from grouped data to individual letter scoring.
+
+## Reasonable Solution
+
+The code snippet provided in TypeScript represents a function named transform. 
+This function takes in an object oldData, which has keys representing point values (as strings) 
+and values as arrays of strings (letters associated with those point values).
+
+The function iterates through the oldData object, 
+assigning each letter (converted to lowercase) to 
+its corresponding score in the newData object. 
+The return value of the function is an object where keys are 
+lowercase letters and values are the associated point values (as numbers).
+
+```typescript
+export function transform(oldData: { [key: string]: string[] }): { [key: string]: number } {
+    const newData: { [key: string]: number } = {};
+
+    for (const [score, letters] of Object.entries(oldData)) {
+        letters.forEach((letter: string) => {
+            newData[letter.toLowerCase()] = parseInt(score);
+        });
+    }
+
+    return newData;
+}
+```