Add support for IShField ValueType Label coming over API 2.5 in 15.1/Alf1

[ddemeyer]

One of the UX improvements in Tridion Docs 15.1/Alf1 release is the availability of a User's Display Name throughout user interfaces. Technically this means that the public API had to be extended in a non-breaking way to support delivering these values. The choice was made to add a new valuetype attribute on the the <ishfields> metadata containers in API 2.5 called Label.

User Display Name can now be returned on User Card Reference fields. So where you used to be able to retrieve Value/Element/Id on fields like FAUTHOR or FTRANSLATOR, you can now also request the non-unique Label (the user's display name)

ValueType	Value
User Value	ddemeyer
User Element	VUSERDDEMEYER
User Id	45665
User Label (new since 15.1/Alf1)	Dave De Meyer

Same idea works to retrieve Logical Object Titles on Logical Content Object Reference fields. So where you used to be able to retrieve Value/Element/Id on fields like FMASTERREF (root DITA Map on a Publication Version) or FISHRESOURCES (library DITA Topics on a Publication Version), you can now also request the non-unique title (the object's FTITLE field)

ValueType	Value
Map Value	GUID-A...Z
Map Element	GUID-A...Z
Map Id	45465
Map Label (new since 15.1/Alf1)	Release Notes Root Map

For ISHRemote it means that the following things need to be reviewed

• [ ] Set-IshMetadataField should probably throw as no write operation is allowed as Dave De Meyer is not a unique identifier (while value ddemeyer or element VUSERDDEMEYER is guaranteed to be unique).
• [ ] Set-IshMetadataFilterField should probably throw as filtering is not implemented on a lookup field (like FISHUSERDISPLAYNAME and FTITLE).
• [ ] Set-IshRequestedMetadataField should work
• [ ] Set-IshRequiredCurrentMetadataField should probably throw as value checks is not implemented on a lookup field (like FISHUSERDISPLAYNAME and FTITLE).
• [ ] Get-IshMetadataField should work
• [ ] $ishSession.DefaultRequestedMetadata should be verified to potentially add Label by default, but this only for 15.1/Alf. What happens if you use Label on 15.0 and lower instances - throw?
• [ ] $ishSession.StrictMetadataPreference variations could explicitly or silently remove Label usage depending on the target instance server version

[ddemeyer]

Put more thought into it...

• DisplayName can already be done, with a lookup over Find-IshUser explicitly asking for the FISHDISPLAYNAME field in the PowerShell process perhaps a post-routine over Add-Member cmdlet
• Title on Content Object card references like FISHRESOURCES on a publication, this is an edge case

Mostly concerned that this would complicate the code that much that switching to future public OpenApi without little-to-none breaking changes might become harder instead of easier - what is -ValueType Label worth on OpenApi, nothing really, it is implicit.