feat: proxy bypass with WebSocket

[sapphi-red]

Description

#13218 made Vite's internal WebSocket connection to be able to be proxyed to other servers. But that made it impossible to proxy WebSocket connections while not proxying the internal WebSocket connection (See the table below).

Protocol	Path	Proxy?	Remarks
HTTP	/	⭕
HTTP	/aaa	❌
WS	/	⭕	WS connection to backend
WS	/aaa	❌	Vite's internal WebSocket connection. This will be proxyed without this PR.

This PR makes proxyOptions.bypass to be called for WebSocket connections and make that possible.

An alternative is to change the WebSocket protocol to vite-hmr-${randomid} instead of vite-hmr and proxy all WS connections except connections with vite-hmr-${randomid}. Proxying other Vite server's WS connection is possible because other Vite server would have a different randomid.

fixes #17973

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