The template for the instance detail overview uses Django template
filters to define a default value for metadata with an empty value.
This usage looks magic and does not work with Django 4.2.
It looks like this is an undocumented/unspecified behavior.
This commit changes it to use {% if %} template syntax instead of
depending on the unspcified behavior.
Closes-Bug: #2040129
Change-Id: Ida5b2a721f2657347c174e386d2e023dffd64b1b
5c61331ff2