[TASK] Improve documentation

[LeoRaasch]

Description

The documentation of the query plan serialization on this side of the project should be improved by adding additional comments / cleaning up messy comments.

Acceptance Criteria

Improve documentation for:

• --visualizePlan flag
• logical plan serialization
• pipeline plan serialization
• plan graph proto files
• BenchmarkResult.json creation
• BenchmarkResult.py