Connection tester

[KaraMelih]

What does this PR do?

• It actually does two things (that I should have separated)
• 1st it fixes the wrong filename selection when a plugin script was used. Before, it was first making a file name "0-SNEWS_ALERT..." saving this, and when plugin script was called it was making a new file name by increasing the count "1-SNEWS_ALERT...". If fixed this by returning the saved file name to the plugin.
• 2nd I made a CLI tool for testing connection snews_pt test-connection The logic behind the connection is (following this issue https://github.com/SNEWS2/SNEWS_Coincidence_System/issues/11) I open two streams one for publishing and one for reading. I add a time stamp and submit a "test-connection" message, within the other stream I read the last message within last 5 seconds, if the time stamp in that message is the same with the one we published, I display connection verified message.

[KaraMelih]

This PR checks the connection to the kafka brokers, however using the same logic and making some adjustments to the snews_cs backend we can also test connections to the servers. In that case server should submit another message when it sees "test-connection" in the id, and we try to see that message on the user side.