Switch to Go's errors.Join from multierror

[ka3de]

As part of the tasks done prior to the merge with k6 core in #734 we got rid of Hashicorp's multierror dependency in favor of our custom implementation that fulfilled our current use case.

This implementation should be replaced by something simpler, and we should also reevaluate if there is a need for multierror in remote_object implementation, which currently is the only component that uses it, or overall in xk6-browser codebase.

A possible candidate to replace the current implementation would be to use Go's support for wrapping multiple errors introduced in v1.20.

Tasks

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1. Remove multierror and refactor to Go errors.Join #850
   maintenance refactor +2
   
2. Add browser 850 and other Go 1.20 PRs to release notes k6#3605
   +0