Previously an empty input (just pressing enter) was only allowed for multiple-choice
options that did not have the Exclusive property set. With this change the existing
Required property is introduced into the multiple choice handling, so that one can have
Exclusive and Required options where only a value from the list is allowed, and one can
have Exclusive but not Required options where an empty value is accepted but any
non-empty value must still be matching an item from the list.
Fixes#5549
See #5551
This also factors the config questions into a state based mechanism so
a backend can be configured using the same dialog as rclone config but
remotely.
Restructuring of config code in v1.55 resulted in config
file being loaded early at process startup. If configuration
file is encrypted this means user will need to supply the password,
even when running commands that does not use config.
This also lead to an issue where mount with --deamon failed to
decrypt the config file when it had to prompt user for passord.
Fixes#5236Fixes#5228
This splits config.go into ui.go for the user interface functions and
authorize.go for the implementation of `rclone authorize`.
It also moves the tests into the correct places (including one from
obscure which was in the wrong place).
