closes #1012 - allow string[] to be used in an @Extension

[oliver-brm]

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Closing issues

Closes #1012.

Test plan

The added test suite ValidExtensionControllerGenerator makes sure that @Extension declarations, similar to those we need to feed into Amazon API Gateway, do work. It's somewhat a double-check because without allowing string[] in @ExtensionType, TypeScript would not compile at all.

[WoH]

We already have specs for existing extensions for both v2 and v3 of OpenAPI.
Can you please extend these? Not throwing is too weak of an assertion.

Refs:

• https://github.com/lukeautry/tsoa/blob/master/tests/fixtures/controllers/methodController.ts#L158
• https://github.com/lukeautry/tsoa/blob/master/tests/unit/swagger/schemaDetails.spec.ts#L495
• https://github.com/lukeautry/tsoa/blob/master/tests/unit/swagger/schemaDetails3.spec.ts#L2144

[oliver-brm]

@WoH OK, I added the fixture/tests to methodController.ts, schemaDetails.spec.ts, schemaDetails3.spec.ts and metadata.spec.ts.

[WoH]

LGTM, thanks for submitting a PR! 🚀