feat: add asset source information & filters

[SvSven]

This adds the asset source name and ID to the asset detail dialog and allows for filtering on those fields.

Our editors use a digital asset management system for company wide asset management, for which we have made a custom asset source in order to import assets into Sanity. This feature allows them to more easily find and keep track of imported assets between the Sanity and company DAM; which is useful for when they for example have to remove a specific asset for GDPR reasons or find out where a specific asset has been used.

[robinpyon]

Hey @SvSven, thanks so much for taking the time to submit this PR (I've been following the thread in slack too)

Regretfully this isn't something I'd be able to merge right now. Despite it being non-breaking, these fields aren't applicable to all users. My recommendation for now is that you use a fork of this repo with whatever custom fields (and search facets) you require.

However, this request again highlights a greater feature which this plugin has been sorely lacking – the ability to customise your own fields on sanity assets (and by extension, search facets too)

This is something I'll be looking into very soon, so please sit tight in the meantime!

[SvSven]

Thanks for the feedback! While not ideal, we'll use a fork to support this feature until we are able to customize those fields and filters in the plugin itself, as this is requirement from a GDPR standpoint 👍