Document webpack change: feat: allow template strings in `output.devtoolNamespace`

[webpack-bot]

A pull request by @snitin315 was merged and maintainers requested a documentation change.

See pull request: webpack/webpack#18480

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What kind of change does this PR introduce?
Fix #18243

Did you add tests for your changes?
Yes

Does this PR introduce a breaking change?
No

What needs to be documented once your changes are merged?
output.devtoolNamespace also accepts template strings like [name].