Change asset_root in production
Change asset_root in production

This will change `/etc/govuk/env.d/GOVUK_ASSET_HOST` and
`/etc/govuk/env.d/GOVUK_ASSET_ROOT` on every machine.

I don't think this will restart every application but it may do, so
it requires care when deploying.

These 2 hostnames are served by the same backend so changing them will
make no difference at all.

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