New external crons that runs individualy by campaign

[etruel]

Inside campaign editing screen
Add an option to create new URLs to individually call campaigns from external crons.
Should hide the Cron Metabox when activated.
Similarly on how is working the wpematico cron, but in this case just that campaign will be called.

With Password it adds &code=mypass

For external cron exclusive per campaign, we can add an option below "Log file for external Cron"

[ ] Activate External Cron Exclusive per Campaign feature.

Activating this will Add a metabox inside campaign editing screen with a checkbox to activate external cron for this campaign, and will show the link and the command for the external cron like

https://netmdp.com.ar/wp-admin/admin-post.php?action=wpematico_cron&campaign_id=14&code=c4ebb1dc

The entire cron and execution schedule of that campaign would depend on the external call.
This mean that the Activate campaign option and Cron scheduled inside campaign will be deactivated or ignored.