`remote-build` lacks support for selecting Snapcraft channel

[Michał Sawicz]

Launchpad has API to choose a channel for Snapcraft:

https://launchpad.net/+apidoc/devel.html#snap_build

> channels (writeable)
> Source snap channels to use for this build.
> A dictionary mapping snap names to channels to use for this build. Supported snap names: 'core', 'core18', 'core20', 'core22', 'core24', 'snapcraft', 'snapd'

Would be good to expose that on `remote-build`, and even better - default to whatever the local Snapcraft channel is, if possible.

[Callahan Kovacs (mr-cal)]

This API field is defined in https://github.com/canonical/craft-application/blob/24695b5d9df81b73e16e5728865b41edfca364e5/craft_application/launchpad/models/recipe.py#L57, but it is not exposed to snapcraft.

It will need to be exposed in craft-application and snapcraft will need to be able to set it.

The same implementation should be used for charms as well (for the `charm_recipe_build`).