fix(admin-ui): Admin ui code templates

[tschortsch]

Description

This PR fixes some syntax errors in the admin-ui code templates. (See #2544)

Checklist

• I have set a clear title
• My PR is small and contains a single feature
• I have checked my own PR

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[michaelbromley]

Thank you!

[tschortsch]

I've just seen that there might we even more issues in the code templates. Probably by changes the interfaces of the addXY functions over time. Eg.

addNavMenuSection(
   {
      id: 'my-menu-item',
      label: 'My Menu Item',
      routerLink: ['/extensions/my-plugin'],
   },
   '${locationId}',
),

doesn't have a routerLink property directly but inside the items array. I'll try to fix those as well as soon as possible.