Implement the load generator core functionality

[belimawr]

The goal is to implement the core functionality of a load generator to test the shipper and be the firs implemented input.

Design

• Look into the current documentation about the shipper performance testing: elastic/elastic-agent-shipper#57
• Investigate if https://github.com/elastic/stream can be used as our core

Acceptance criteria

• Configurable throughput
• Set the number of events or a constant rate/throughput
• Timestamp increments can be configured independently from throughput (e.g: 100 events with a timestamp delay of 1s between each other can be generated/sent as fast as possible)
• Random data generated, the first implementation can have a single format
• Unique ID on every message (can be something log friendly like xid)

Nice to have:

• Configurable data format, ideally based on Elastic-Agent integrations