Support entry in vue-cli-service serve

[miljan-aleksic]

What problem does this feature solve?

Currently vue-cli-service will assume the entry file is on src/main, while does seems convenient a project may have another structure or even two different apps. Having the option to tell vue-cli-service where is the entry would solve it. Using vue serve instead is not convenient as it use globals.

Additionally and on the same line, vue-cli assumes is on the project root and doesn't support yarn workspaces. Having a way to tell him where the main node_modules are would give it more flexibility.

What does the proposed API look like?

vue-cli-service serve my/entry.js