Add `accessMethod`-derived fields to support archive browsing

[StepanBrychta]

Archive browse designs include a few new access-related fields, including:

• Total count of items within an archive collection that are available online (see here)
• Per-item access information in the collection contents table (see here)

These fields are derived from the access method field, which has the following five allowed values: OnlineRequest, ManualRequest, NotRequestable, ViewOnline, OpenShelves

We should make this field filterable and aggregatable to support the features above.