Fix html report generation and write monitor json result

[julienduchesne]

• Ready for review
• Follows CONTRIBUTING rules
• Reviewed by Snyk internal team

What does this PR do?

• Fixes the HTML report feature. Currently, the output file is text not json but jq is run on it. It returns parse error: Invalid numeric literal at line 2, column 8 Failed to run the process ...
• Adds a snyk-monitor-result.json

[adrukh]

@julienduchesne this is indeed an important fix, but it highlights a shortcoming in our docker image entrypoint. We aimed at allowing monitor to run after test via the MONITOR env var, and broke the flow where a user just wants to run snyk monitor via the docker image.

Your suggestion addresses this issue, but I wonder whether it breaks the ability to run snyk test via the docker image, expecting human-readable and not JSON output...

[julienduchesne]

We would have to run snyk test twice to get both the json result and the human readable output. Would that be acceptable?