feat: add an option to not start a websocket server

[sheremet-va]

Description

This PR adds an option server.ws that can only be equal to false. I wasn't sure if I should change server.hmr type (make it nullable like the watcher?), so I added a new one. If we want to use server.hmr, we would need to replace all server.hmr === false.

Also, do we want to document this option?

Closes #14328

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines, especially the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Update the corresponding documentation if needed.
• Ideally, include relevant tests that fail without this PR but pass with it.

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[bluwy]

@sheremet-va Is this something you'd like to get out soon? I think we can merge this in a patch since it's not a big change, otherwise if it's not urgent we can queue this for the next minor.

[sheremet-va]

@sheremet-va Is this something you'd like to get out soon? I think we can merge this in a patch since it's not a big change, otherwise if it's not urgent we can queue this for the next minor.

I am fine with it being in a minor. I am using a workaround by assigning a dummy hmr.server for now.