JavaScript assets could be cached across Linkerd releases, showing an
out of date ui, or a broken page.
Modify the webpack build pipeline to add a hash to the JS bundle
filename. Move all logic around webpack-dev-server state from Go into
JS, via a templatized index_bundle.js file, generated at build time.
Disable caching of index_bundle.js in Go, via a `Cache-Control` header.
Fixes#1996
Signed-off-by: Andrew Seigner <siggy@buoyant.io>
Andrew Seigner