Fix(useFlip): prevent registerPlugin from running on server

[evertmonk]

I got the following error in a project using this hook.

web:dev:  ⨯ TypeError: gsap__WEBPACK_IMPORTED_MODULE_2__.registerPlugin is not a function
web:dev:     at eval (webpack-internal:///../../node_modules/.pnpm/@[email protected][email protected]/node_modules/@mediamonks/react-kit/dist/gsap/hooks/useFlip/useFlip.js:14:35)

After inspecting other hooks I saw that the other hooks have a safeguard to prevent it from running on the server.

if (typeof window !== 'undefined') {
  gsap.registerPlugin(plugin);
}

This safeguard was missing for this hook so this PR is adding that to the useFlip hook.