feat(toolkit-lib): environment variables for 'fromCdkApp'

[rix0rrr]

Add an option env to fromCdkApp, to set the environment variables for the synth'ing subprocess.

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.15%. Comparing base (4068210) to head (428d950).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #443   +/-   ##
=======================================
  Coverage   79.15%   79.15%           
=======================================
  Files          54       54           
  Lines        6889     6889           
  Branches      773      773           
=======================================
  Hits         5453     5453           
  Misses       1418     1418           
  Partials       18       18           

Flag	Coverage Δ
suite.unit	79.15% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 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.