Add event_generator tooling for 5.x indices

[f-galland]

Description

This PR implements a event_generator tool for missing indices:

• fim
• inventory-packages
• inventory-processes
• inventory-system

Since the command plugin's event generator was outdated and not working correctly, it received an update adapting it to the current status of the plugin.

It also includes improvements to existing event generators, replacing general warnings suppression to just urllib3 ones, and adding default value for the corresponding inputs. Example:

python agent/event-generator/event_generator.py 

How many events do you want to generate? 2
Do you want to inject the generated data into your indexer? (y/n) y
Enter the IP of your Indexer (default: '127.0.0.1'): 192.168.73.4
Enter the port of your Indexer (default: '9200'): 
Enter the index name (default: '.agents'): 
Username (default: 'admin'): 
Password (default: 'admin'): 

Related Issues

Resolves #518

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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