clientgen/typescript: add ? when optional is added

[Delta456]

Fixes #924

[encore-cla]

All committers have signed the CLA.

[github-actions]

Test Results

    2 files  +       1  227 suites  +65   14m 7s ⏱️ - 11m 15s
722 tests +   163  719 ✔️ +   172  3 💤 +3  0 ❌  - 3 
722 runs   - 1 909  719 ✔️  - 1 900  3 💤 +3  0 ❌  - 3 

Results for commit a074c46. ± Comparison against base commit 3c5a103.

This pull request removes 39 and adds 202 tests. Note that renamed tests count towards both.

encr.dev/e2e-tests ‑ TestRun/encore_currentrequest
encr.dev/e2e-tests ‑ TestRun/et_override_user
encr.dev/e2e-tests ‑ TestRun/et_override_user_authdata
encr.dev/e2e-tests ‑ TestRun/experiment_local_secrets_override
encr.dev/e2e-tests ‑ TestRun/fallback_routes
encr.dev/e2e-tests ‑ TestRun/graceful_shutdown
encr.dev/e2e-tests ‑ TestRun/pubsub_method_handler
encr.dev/e2e-tests ‑ TestRun/pubsub_ref
test/svc ‑ TestEndToEndWithApp
test/svc ‑ TestEndToEndWithApp/basic_requests
…

encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/echo
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/invalid
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/raw
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/unauthenticated
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd/echo
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd/invalid
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd/unauthenticated
encore.dev/appruntime/apisdk/api ‑ TestRawEndpointOverflow
…