Google Tag Manager
Merchants often need to ad a simple script to their theme for example to validate ownership. Therefor there should be a possibility to add scripts to the storefront theme. Maybe integrated into the consent tool.
Marco Steinhäuser commented
To point that out: it is not only about Google Tag Manager - many other external services especially in E-Commerce need to have a place for their JS or CSS scripts in header or footer section of the shop pages.
As far as I understood the concept, it is not possible in Shopware to just change the according section in Shopware as a real template override mechanism seems not to be existent. Presently, it is possible to help oneself with a small plugin or app to inject code. Also, there are plugins available out there in the store.
Ways smarter would be to allow inserting these scripts per sales channel (theme-related) from the admin panel. Please see that this option is setup via ACL so that only classified personnel can make changes ;)