PC advertises extensions for item-search but not ogcapi-features conformance classes

[philvarner]

PC advertises:

"https://api.stacspec.org/v1.0.0-rc.1/item-search#fields",
"https://api.stacspec.org/v1.0.0-rc.1/item-search#filter",
"https://api.stacspec.org/v1.0.0-rc.1/item-search#filter:basic-cql",
"https://api.stacspec.org/v1.0.0-rc.1/item-search#filter:cql-json",
"https://api.stacspec.org/v1.0.0-rc.1/item-search#filter:cql-text",
"https://api.stacspec.org/v1.0.0-rc.1/item-search#query",
"https://api.stacspec.org/v1.0.0-rc.1/item-search#sort",
"https://api.stacspec.org/v1.0.0-rc.1/ogcapi-features"

Which indicates that the extensions are only supported on the Item Search endpoints and not the Features /items.
I think all of those extensions are also supported on the Features endpoint, so they need to be advertised.