Add lock to mautic:custom_items:scheduled_export

[kuzmany]

Q	A
Bug fix? (use the a.b branch)	[ ]
New feature/enhancement? (use the a.x branch)	[ ]
Deprecations?	[ ]
BC breaks? (use the c.x branch)	[ ]
Automated tests included?	[ ]
Related user documentation PR URL	mautic/mautic-documentation#...
Related developer documentation PR URL	mautic/developer-documentation#...
Issue(s) addressed	Fixes #...

Description:

Steps to test this PR:

Added lock to prevent command mautic:custom_items:scheduled_export run double time.

1. Open this PR for testing locally (see docs on testing PRs here)
2. Create export for large object database and run mautic:custom_items:scheduled_export
3. Run again mautic:custom_items:scheduled_export
4. You should see lock warning Script in progress. Can force execution by using --bypass-locking.

[acquia-stalebot-platauto]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[acquia-stalebot-platauto]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Please remove the stale label to avoid it being closed. Thank you for your contributions. More info: https://github.com/acquia/devops-github-administration/blob/main/docs/operations_related_to_repositories.md#acquia-stale-bot