Build: Migrate @storybook/postinstall and @storybook/router to strict TS

[kuriacka]

Issue #22176

What I did

Migrate @storybook/postinstall and @storybook/router to strict-ts

How to test

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[kasperpeulen]

Thanks @kuriacka!
Can you rebase them on the latest next! (Or merge next in)

[kuriacka]

@kasperpeulen Rebase done.

[kasperpeulen]

LGTM!

[jonniebigodes]

@kuriacka, one thing left to address as part of this initiative and the amazing work you did by helping us convert Storybook's packages to allow stricter TypeScript support. If you're ok with it, can you message me on our Discord server (same username) so that I can follow up with you?

Hope you have a fantastic day.

Stay safe

[kuriacka]

@jonniebigodes, I was unable to send you message via Discord. How can I help you?