feat: Add mailbox_cleaner.py script for automated cleanup

[drsound]

Adds a Python script to expunge old emails from specified mailboxes (e.g., Trash, Junk) and remove empty subfolders. Supports single-user, all-user, and dry-run modes.

Contribution Guidelines

• I've read the contribution guidelines and wholeheartedly agree them

What does this PR include?

Short Description

Adds a Python script (mailbox_cleaner.py) located in helper-scripts/ designed to automatically clean up old emails from specified mailboxes (defaults to Trash, Junk) for single or all users in a Mailcow installation. It includes features like configurable retention days, dry-run mode, and automatic deletion of empty subfolders within the target mailboxes. Intended for cron job execution.

Affected Containers

• None (This PR only adds the script to the repository structure; it does not modify any existing container images or configurations.)

Did you run tests?

What did you tested?

• Tested script execution with Python 3.x.
• Tested against a live Mailcow instance.
• Validated --user <email> argument for single-user processing.
• Validated --all argument for multi-user processing.
• Validated --dry-run functionality (logs actions without performing them).
• Tested default --days-back 30 and custom values.
• Tested default mailboxes (Trash, Junk) and custom --mailboxes argument.
• Verified correct identification and processing of target mailboxes and their subfolders.
• Verified expunge logic based on savedbefore <days>d.
• Verified deletion logic for empty subfolders within target mailboxes.
• Verified that non-empty subfolders and top-level standard folders are not deleted.
• Checked standard and --debug logging output.

What were the final results? (Awaited, got)

• Awaited: Script correctly identifies target mailboxes/users, simulates actions in dry-run, expunges emails older than the specified period, and deletes empty subfolders under target mailboxes in normal mode.
• Got: The script performed exactly as awaited in all tested scenarios. Dry-run accurately predicted changes. Normal execution successfully cleaned up old emails and empty specified subfolders without affecting other data. Logs provided clear information.

[DerLinkman]

See comments

[drsound]

Search & replace done! :-)

[drsound]

Hi, this PR seems stale. Is any additional action required from my side?