This additional/removable code offers an opportunity for a product
to be fully defined in the store, but not shown as available,
upcoming, new, etc (because it is disabled) until the product
available date at which point it appears in the store as an
enabled product ready for the customer to see and/or purchase.

These functions were moved into products_functions by discussion/request in zencart#2720.

Ensures loading of `functions_products.php` and enables disabled product that were marked as having a future products_available_date where the current date is equal or beyond the date it was to become available.

As requested in zencart#2720, the call to the functions to enable disabled product was moved into: `includes/init_includes/init_special_funcs.php` which eliminated the need for loading `includes/init_includes/init_special_funcs_disabled_upcoming.php` and therefore eliminated the need for this separate config file.

This functionality was moved into `includes/init_includes/init_special_funcs.php` as discussed in zencart#2720.

Allow the enablement of product that have a historical product_available_date if the constant is defined and set to support enablement of this feature.

Consideration was given for testing/checking against `!= '0'`; however, seems that such an option would only be necessary to support some sort of third, fourth, etc... condition which is not clear what it may be and therefore likely would require modification of this area of the code if generated.  By the check specifically against `== '1'`, whatever defines it (file or database) if it is equal to 1 then this area of code will execute.

Alternatively, for those that do mass installations, if they choose not to include the option in the database or choose to remove it, then code will continue to operate without execution of this feature.

Made spacing of 4 spaces and removed parentheses around require/require_once calls.  Also corrected an issue with the earlier incorporation of `functions_products` where the closing parenthesis was omitted.

Adds the admin control for enabling the feature to enable product that are in the disabled status and has a `products_available_date` in the database that has come to be or has passed.
Default set to `0` to allow store owners to enable this feature potentially after a review of the database/product.  This is to prevent the sudden appearance of disabled product that happened to have a date entered in the `products_available_date` field.

Associated with zencart#2720.

Although original code had been adapted from other similar (but more complex) queries, the additional parentheses are unnecessary and I believe this was pointed out in earlier code review.

Use `foreach` instead of the older combination of `while (!$variable->EOF)` with `$variable->MoveNext()`
This also eliminated the need to check for the number of records returned.

As requested in the PR discussion, updated the `configuration_title` and `configuration_description` to try to provide an improved explanation of what this feature does.

Note, that as a result of working through this explanation, identified that enablement occurs without consideration of stock quantity or any other potential reason one may wish the product to remain disabled.  This is a further reason why the default is for this feature to be off upon install/upgrade so that consideration may be given to data modification and/or the desire to turn it on.

As requested in the PR discussion, updated the `configuration_title` and `configuration_description` to try to provide an improved explanation of what this feature does.

Note, that as a result of working through this explanation, identified that enablement occurs without consideration of stock quantity or any other potential reason one may wish the product to remain disabled.  This is a further reason why the default is for this feature to be off upon install/upgrade so that consideration may be given to data modification and/or the desire to turn it on.

In preparation for future updates to the date/time processing
to use NULL instead of the historical default of `'0001-01-01 00:00:00'`
choosing to use NULL instead which is supported by the field.

This reduces one change to the overall system.  Check for whether
to process the record still compares against `'0001-01-01'`
in the event other "systems" clear the field to be appear as
empty.

For new installation (not using a previous database), set this to
automatic to enable product that are disabled and have a future
date.  For upgrades left this as Manual so that a database update
will not automatically enable product that were disabled but had
a future date.

Previous operation without this additional feature would have
left the product disabled from viewing on the store until the
product were enabled.