How to configure webpack dev server to serve extensionless files as 'text/html' - vue.js

Question

Problem
In development, serving files without an extension (e.g. /region) are being served with mimetype `application/octet-stream'. Desired state is to serve these with mimetype 'text/html'.
Context
Writing a multipage application using Vue3. Upgraded #vue/cli and that upgraded webpack from 4 to 5. Serving extensionless files did not have this issue using webpack4's dev server.
In production this isn't a problem as the webserver there is configured to serve these files with the 'text/html' mimetype.
Dependency versions
node 16.13.0, webpack 5.64.1, webpack-dev-middleware 5.2.1, #vue/cli 5.0.0-rc.0
Webpack5 config
entry: {
region: [
'/home/alice/workspace/vapp/src/pages/region/main.js'
],
plugins: [
/* config.plugin('html-region') */
new HtmlWebpackPlugin(
{
title: 'Region',
scriptLoading: 'defer',
templateParameters: function () { /* omitted long function */ },
chunks: [
'chunk-vendors',
'chunk-common',
'region'
],
template: 'src/pages/region/region.html',
filename: 'region'
}
),
]
Attempts
Supplying custom extension to mime type mapping works for custom extensions just fine, e.g. 'foo': 'text/html' will serve region.foo as html. However, there doesn't appear to be a way to specify a mime type for files without an extension. None of the these mimeTypes entries have been successful.
// webpack.config.js
devServer: {
devMiddleware: {
mimeTypes: {
'': 'text/html',
false: 'text/html',
null: 'text/html',
default: 'text/html',
}
}
}