We can only validate MinItems >= 1 (equiv to "Required") during
decoding, as dynamic blocks each only decode as a single block. MaxItems
cannot be validated at all, also because of dynamic blocks, which may
have any number of blocks in the config.
If a block was defined via "dynamic", there will be only one block value
until the expansion is known. Since we can't detect dynamic blocks at
this point, don't verify MinItems while there are unknown values in the
config.
The decoder spec can also only check for existence of a block, so limit
the check to 0 or 1.
We need to make the collection itself be a tuple or object rather than
list or map in this case, since otherwise all of the elements of the
collection are constrained to be of the same type and that isn't the
intent of a provider indicating that it accepts any type.
Any value that is not set in the configuration should decode as a Null
value. Unknown should still be returned if a computed value expression
is unknown.
The "config" package is no longer used and will be removed as part
of the 0.12 release cleanup. Since configschema is part of the
"new world" of configuration modelling, it makes more sense for
it to live as a subdirectory of the newer "configs" package.
