Drop-down list for Related Links

[stain]

Building on from #12 then instead of just a free-text field for "Related Links" (former "Discussion Channel") it would be nice to have a suggested list of link relations for the user to select from.

Part of this idea is that given a list of suggested links like documentation the user is more likely to fill it in than if it's all free-form.

These kind of links would be part of the value added by Workflow Hub - in theory people can put them in their GitHub README but frequently they don't.

Zenodo calls this "Related Identifiers" - see right margin on https://zenodo.org/record/4012124 for example.

Our drop-down list could also be based on (or be compatible with) DataCite schema's relationType although some of these may not make sense on workflows. (They may make sense on other SEEK types)

Mockup (based on Zenodo's form):

New in latest DataCite is also typing the resource at the other end - this is often just as useful:

However we may need "Other" as well with a text-field to fill in.

Here is the list Zenodo use:

relation	label
datacite:isCitedBy	cites this upload
datacite:cites	is cited by this upload
datacite:isSupplementTo	is supplemented by this upload
datacite:isSupplementedBy	is a supplement to this upload
datacite:references	is referenced by this upload
datacite:isReferencedBy	references this upload
datacite:isNewVersionOf	is previous version of this upload
datacite:isPreviousVersionOf	is new version of this upload
datacite:isContinuedBy	continues this upload
datacite:continues	is continued by this upload
datacite:isPartOf	has this upload as part
datacite:hasPart	is part of this upload
datacite:isReviewedBy	reviews this upload
datacite:reviews	is reviewed by this upload
datacite:isDocumentedBy	documents this upload
datacite:documents	is documented by this upload
datacite:compiles	is compiled/created by this upload
datacite:isCompiledBy	compiled/created this upload
datacite:isDerivedFrom	is the source this upload is derived from
datacite:isSourceOf	has this upload as its source
datacite:isIdenticalTo	is identical to this upload
datacite:isAlternateIdentifier	is an alternate identifier of this upload

For us this upload is this workflow. See https://schema.datacite.org/meta/kernel-4.3/doc/DataCite-MetadataKernel_v4.3.pdf#page=46 (page 46) for full DataCite list.

As commented in #12 if we have the types of links we can not just present them in nicer ways but also provide them programmatically in the RO-Crate, BioSchemas markup and in DataCite export.

Other more generic link relations registries are IANA link relations which is used in <link rel="cite-as" href="https://doi.org/10.1234/abcd"> and <a rel="preview" href="thumbnail.png"> in HTML and equivalent Link: HTTP header although they are probably more important for internal site navigation.