Ignore tsconfig provided by smithy-typescript, and extend root TSConfig while running `generate-clients`

[trivikr]

Is your feature request related to a problem? Please describe.
The PR #1297 creates root TSConfig for packages/*, but it doesn't apply to clients/* as the clients generated by smithy-typescript should be able to work independently. They need not be part of a monorepo setup.

Because of this, the internal dependencies are not navigable in clients as shown in the screenshot

Screenshot

Describe the solution you'd like

Let smithy-typescript emit tsconfig as it wants, but it should be overriden to extend root TSConfig by generate-clients command.

Describe alternatives you've considered
Sticking with individual TSConfig files for clients

[trivikr]

Closed by mistake.

smithy-typescript will emit a separate TSConfig, as clients should be able to work on their own in an independent repository. The ask is to use central TSConfig in aws-sdk-js-v3 monorepo.

[trivikr]

Root tsconfig was added in #1297