Feature Request/Idea: Allow creation of 'invisible' or 'internal' metadata

Overview of the Feature Request
Allow administrators to create metadata templates with optional or mandatory metadata fields for users to add metadata that will not become visible on the dataset's landing page upon publication. Those metadata should only be visible to administrators and/or through the API.

Request based on this discussion:
https://groups.google.com/g/dataverse-community/c/sXTNPfDCJS4/m/SP3lB2YlBAAJ

What kind of user is the feature intended for?
(Example users roles: API User, Curator, Depositor, Guest, Superuser, Sysadmin)
Mainly (sub) dataverse administrators.

What inspired the request?
We are looking for some way of 'flagging' datasets for future administrative purposes. Something like:

• A copy of the metadata of this dataset should be sent to...
• A copy of the whole dataset should be sent to...
• This dataset should be updated when...

There might be different ways of achieving this, but we think that 'invisible' metadata fields would be easiest. This would also allow for adding 'internal comments' to a dataset.

What existing behavior do you want changed?

Any brand new behavior do you want to add to Dataverse?
New property for metadata fields.

Any related open or closed issues to this feature request?

Start by reading the linked community discussion and tracing how metadata templates, dataset publication, landing-page display, and API responses currently handle fields. Define the administrator-facing behavior and verify that internal fields stay out of the published landing page while remaining available to administrators and through the API.