Update to webpack-dev-server 4.15.2

[pjonsson]

What this PR does

This fixes security issues
in dependencies.

This also requires updating webpack-cli
to version 4, so use the latest version
available.

Test me

I think this is tested by CI?

Checklist

• There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• I've updated relevant documentation in doc/.
• I've updated CHANGES.md with what I changed.
• I've provided instructions in the PR description on how to test this PR.

[na9da]

@pjonsson - Thanks for the PR.

Are you able to pull in the latest main to fix the conflicts?

[pjonsson]

@na9da rebased to latest main. It's getting late here so I won't be at the computer much longer tonight, is there some other old PR I should rebase?

[pjonsson]

@na9da Thanks! I'm not sure I understand the intricacies of interdependencies with Terriamap, but I just made a similar PR in that repository.