Generated tsconfig.json should set `strict` by default

[Brendan Linn]

At head, running miskweb new ... generates a tsconfig.json that does not include the strict tsc options. This significantly reduces the value of the TypeScript type system, since any variable/parameter/etc. can have a null or undefined value, regardless of its declared type.

I just went through a migration on an internal project where I set strictNullChecks manually, via the rawTsconfig field in miskTab.json. I had to fix a couple hundred type annotations. Enabling these options by default for new projects will get this right from the start.

(Arguably, the real issue is why tsc isn't strict by default, but that ship has sailed.)

[Ricardo Mariano]

This should be in https://github.com/cashapp/misk-web

[Brendan Linn]

Oops, thought it was part of this repo.