Change host_id cardinality to 1..n

[allysonlister]

Currently there is only a 'url' field for hosts.

However, it would be fantastic if we could instead have a host_id field that is of the same type as other identifiers within the framework (e.g. grant_id) with a cardinality of 1...n instead. Having a changeable url as the primary identifier of a repository is not a great idea. Modifying this to a host_id would allow us to reference the host with e.g. the FAIRsharing DOI of the repository (which a number of DMP tools will have and which provides unambiguous and persistent identification of a repository) but also other ids, e.g. the homepage url (as currently present in this framework), direct DOI of the database, or other appropriate identifiers.

Please can I suggest replacing url with host_id with 1...n cardinality? Thanks!

(tagging @TomMiksa)