docs(dev-server): add transportMode docs and examples

[knagaitsev]

describe your changes...

devServer.transportMode: #3239

I think that, rather than having large custom implementation examples in here, we should link to implementation examples in webpack-dev-server/examples.

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[EugeneHlushko]

Hi @Loonride
requesting changes here, appreciate committing suggestions if you agree with them, otherwise lets discuss

[knagaitsev]

I did a bit a bit of minor reorganization for the new transportMode.client and transportMode.server sections.

[knagaitsev]

@EugeneHlushko Currently the types I have are:

devServer.transportMode:
string = 'sockjs': 'sockjs' | 'ws' object

devServer.transportMode.client:
string path

devServer.transportMode.server:
string path function

Should path be there, or should we just let that fall under string? If you think these are not specific enough, could you suggest how to make it fit in with the Writer's Guide guidelines?

• Could string for the client and server be changed to string = 'sockjs': 'sockjs' | 'ws' | path?
• Could I do function: class? I just need something making it clear that providing a plain function like server: () => {} will not be sufficient

[EugeneHlushko]

Yes, i think it looks very good now

[EugeneHlushko]

Thanks!