fix: support `devServer.server` option, avoid deprecation warning

fix: support `devServer.server` option, avoid deprecation warning · vuejs/vue-cli@558dea2

fix: support devServer.server option, avoid deprecation warning

Closes #7024 Fixes #7118 I choose to not merge the PR because I don't want add additional ways to configure https for dev server (`--http2` command line argument, `process.env.HTTPS`, etc.) In the current implementation, `spdy` can only be configured by setting `{ devServer: server: { type: 'spdy' } }`. This is a deliberate choice, because SPDY support in Node.js 15+ is broken anyway. I don't want bother refactoring the old code to accommodate this broken feature.