[Browse] Show Browse models link in nav only when there are models (#43286)

frontend/src/metabase/browse/components/BrowseModels.tsx

frontend/src/metabase/browse/test-utils.ts

frontend/src/metabase/common/hooks/use-fetch-models.tsx

frontend/src/metabase/common/hooks/use-has-models.tsx

.../LoadingAndErrorWrapper/DelayedLoadingAndErrorWrapper.tsx

...tabase/nav/containers/MainNavbar/MainNavbar.unit.spec.tsx

...iners/MainNavbar/MainNavbarContainer/BrowseNavSection.tsx

...tainers/MainNavbar/MainNavbarContainer/MainNavbarView.tsx

frontend/src/metabase/nav/containers/Navbar.unit.spec.tsx