remote build: provide a way to set application snap channel

[lengau]

What needs to get done

Probably an environment variable(?) that tells Launchpad what snap channel(s) to use for remote builds.

Why it needs to get done

Enable users to use non-default channels with remote build, especially using the edge channel.

[syncronize-issues-to-jira]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-2910.

This message was autogenerated

[lengau]

With this implementation, snapcraft and charmcraft remote-build tests should run those tests on the edge channel.