Set metatag parent programmatically (inherited value)

Problem/Motivation

Currently, if we set a metatag value as an empty string via UI, this value inherits the parent value (e.g. global, canonical). Unfortunately, this is only the case on the metatag edit form, because the child metatag gets the parent value on submit.

If we set the child value programmatically empty, we won't get the parent fallback, but instead the ouput of the metatag is skipped entirely (similiar to <none>). This is quite confusing and can lead to unexpected behavior. It would be nice if we can connect the metatag and its parent programmatically, so that the ACTUAL value of the metatag stays empty, but we use the parent value as a fallback.

This way, we could also easily set the parent value as a placeholder in the UI (see ✨ Inherit parent metatags as placeholder in override forms Active ).

Steps to reproduce

Proposed resolution

Fix it.

Remaining tasks

User interface changes

API changes

Data model changes