[browser] dotnet watch for wwwroot folder

[pavelsavara]

I made a change to wwwroot\index.html and expected that
A) browser would reload the page (restart wasm app is OK)
When it didn't work, I hit reload on the browser, but
B) I was served old version (I have cache disabled)
restarting dotnet watch helped.

[dotnet-policy-service]

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