refactor!: Rename template to generate and move rebase/upgrade under switch (#116)

This updates the `template` subcommand to be `generate`. The `template`
usage will continue to work as an alias to `generate`. A new `switch`
command is added that will manage both `rpm-ostree rebase` and
`rpm-ostree upgrade` and is fully replacing the respective subcommands
as a breaking change.

The new `switch` command is under the feature flag `switch` and will
currently only build for the `main` branch builds until it is moved as a
default feature (`v0.9.0`).

Closes #159

src/lib.rs

@@ -8,3 +8,4 @@ pub mod commands;
 pub mod credentials;
 pub mod drivers;
 pub mod image_metadata;
+pub mod rpm_ostree_status;