Remove stdout as format argument #247

Extract of #191
The stdout format should be removed. We will always have some output, but some of it will be behind --verbose flag.

Current behavior

The report summary is printed to stdout based on the persist.format value (set in code-pushup.config.ts or via --persist.format CLI argument).

The default format is ['json', 'stdout']. It is not possible to skip 'json' (we create it anyway regardless, it's needed for the upload). However, if a user wants to get a Markdown report as well, they can easily omit stdout without realizing it. E.g. if they add --persist.format=md, then it removes stdout because the array is replaced.

Proposed change

We print the report summary regardless, and stdout will be removed from possible format values. If the user specifies --persist.format=md, then they will still see the report summary in the stdout.

The results of audits and categories are the most relevant information for the user when they run collect, and the report summary is minimal by design.