Description

This PR is adding a new command to delete custom fields by a command that can be run as a cron job the same as the existing commands that create and update custom fields.

This is the new command: bin/console mautic:custom-field:delete-column --id=[FIELD ID] --user=[USER ID]

If the FIELD ID is not provided, the command will look for fields that were soft-deleted (will be when create_custom_field_in_background is ON). If the USER ID is not provided, the user who modified the custom field the last when they were soft-deleting the field will be used.

There is no change for normal Mautic instances. This command is necessary only for Mautic instances with big leads database tables and busy traffic. Such instances should have the create_custom_field_in_background option set to true and use the background commands to manage custom fields as it modifies the leads table schema which is an expensive (read slow) operation and long running queries on that table while performing the schema change can time out and it could lead to data loss.

📋 Steps to test this PR:

1. Open this PR on Gitpod or pull down for testing locally (see docs on testing PRs here)
2. Test that you can create and delete custom fields as you are used to. The changes in UI directly reflect the changes and the leads table is getting updated with those changes.
3. Now, add this row to the config/local.php file: 'create_custom_field_in_background' => true, and clear the cache with rm -rf var/cache/*
4. When you try to delete a custom fields via UI you can see the field is removed from the UI as before. But it still exists in the database and it is marked for deletion. We could call it soft-deleted.
5. Run bin/console mautic:custom-field:delete-column. Even without the ID the command will find the soft-deleted field and remove it. Only after the command execution the field row in the lead_fleds table is removed and the column in the leads table is removed.