Implement silent mode

[GregoryAlbouy]

Description

With #59, the runner can be integrated in a CI by reading the summary in stdout.
It's an interesting use case, but not ideal for 2 reason:

1. some convenience prints add noise to the output
2. extracting a specific information form the default summary can be tedious, and it might not even contain the desired information

Here we want to address point 1 by allowing users to shut down all convenience prints (runner status, output labels, summary).

Tasks

• Define new config field output.silent and update CLI and file parsers accordingly as well as unit tests. Expected value is a bool
• Update requester so it does not write to stdout if silent == true
• Update output so it does not write to stdout if silent == true
• Determine if there should be an exception for the printed default summary and the printed JSON file path

Suggestions

Notes

• Blocked by #59