Chore(opentelemetry-instrumentation): Add override keyword and access modifier to init()

[lukeina2z]

The init() function is a template method that all classes derived from InstrumentationAbstract must override. Adding an access modifier aligns it with the parent class. Explicitly adding the override keyword improves code readability.

Tests:
npm run compile
npm run lint
npm run test

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.01%. Comparing base (bcec3ef) to head (eb43be4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5838   +/-   ##
=======================================
  Coverage   95.01%   95.01%           
=======================================
  Files         303      303           
  Lines        7943     7943           
  Branches     1607     1607           
=======================================
  Hits         7547     7547           
  Misses        396      396           

Files with missing lines	Coverage Δ
...emetry-instrumentation-grpc/src/instrumentation.ts	95.42% <100.00%> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.