Add a warning if a meta is repeated on the same device

[lorenzo93]

Currently, if a user specifies the same meta (e.g., [image]) multiple times for the same device in the lab.conf configuration file, Kathará silently selects the second option (based on line number) and executes the lab with that setting. This behavior can lead to confusion and unintended configurations.

To address this issue, we need to implement a check for duplicate meta in the lab.conf file. If duplicates are found, a warning should be raised to alert the user about the malformed configuration.

By implementing this check, we ensure that the lab.conf file maintains consistency and avoids any unintended configurations caused by duplicate meta entries for the same device.