WebUI: migrate away from outdated config in ESLint

The following message appears when using the outdated value:
>[@stylistic/eslint-plugin]: You are using deprecated value(boolean) for "allowTemplateLiterals"
>in "quotes", please use "always"/"never" instead.

Also prefer using double quotes over backticks for strings.

PR #23038.

src/webui/www/eslint.config.mjs

@@ -57,7 +57,7 @@ export default [
                 "double",
                 {
                     avoidEscape: true,
-                    allowTemplateLiterals: true
+                    allowTemplateLiterals: "avoidEscape"
                 }
             ],
             "Stylistic/quote-props": ["error", "consistent-as-needed"],