Support returning channel_maps_list from /v1/snaps/search

[Robert Ancell]

/v1/snaps/details/spotify?fields=channel_maps_list works and returns the channel information.
/v1/snaps/search?q=name:spotify&fields=channel_maps_list does not return the channel information.

Please allow the latter to work, this is useful to pass through snapd so searches can be more easily display in GNOME Software. Currently we are either required to do a round-trip for each search result (too expensive) or not know the channel information until a user selects a particular snap (doesn't mesh well with the GNOME Software architecture).

Thanks!

[Robert Ancell (robert-ancell)]

Previous forum discussion for reference:
https://forum.snapcraft.io/t/channel-maps-list-is-empty-when-using-v1-snaps-search-as-opposed-to-using-v2-snaps-details

[Celso Providelo (cprov)]

As discussed previously, attaching channelmap information for all search results is not only expensive but also not entirely useful for consumers. Any decision based on the entire channelmap happens after a snap is selected.