breaking: remove support for webpack-dev-server v4 in `@cypress/webpack-dev-server`

[AtofStryker]

Summary

We should remove support for webpack-dev-server version 4 in @cypress/webpack-dev-server as it is no longer maintained upstream. Continuing to support an unmaintained version increases our maintenance burden and exposes users to potential security and compatibility issues.

Details

• webpack-dev-server v4 is no longer actively maintained by the webpack team.
• Users should migrate to webpack-dev-server v5, which is the current stable and supported version.
• Removing support for v4 will allow us to simplify our codebase and focus on supporting the latest features and fixes.

Migration

• Users who still require webpack-dev-server v4 can continue using older versions of @cypress/webpack-dev-server or follow our migration guide to upgrade to v5
• The migration guide for webpack-dev-server

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Action:

• Remove support for webpack-dev-server v4 in @cypress/webpack-dev-server.
• Update documentation and migration guides accordingly.

Impact:

• This is a breaking change and should be included in the next major release.

[jennifer-shehane]

The work for this is done and will be released in Cypress 15. We'll add a comment here once Cypress 15 is released.