feat: add quiet flag

[eduardoboucas]

Summary

Adds a quiet flag that reduces the output of Netlify Build to a minimum, showing just essential information, errors, and user-generated output.

This is particularly useful for the startDev entry point used by the CLI. Currently, the full Netlify Build information screen is printed on netlify dev, which feels bloated and unnecessary. By making use of the new flag, we'll be able to reduce the output to the essential information.

Before:

After:

[github-actions]

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[lukasholzer]

What do you think about making the quiet the default and instead having a --verbose flag?

[eduardoboucas]

What do you think about making the quiet the default and instead having a --verbose flag?

Interestingly, we already have a --verbose flag (#3934), which seems to be equivalent to --debug.

I agree that this is not ideal, and we should probably have a single flag that allowed you to specify different levels of verbosity. That is a deeper change that I didn't feel comfortable making, to be honest.

As for whether the quiet mode should be the default, I'm not sure I agree. I was planning on using this just on the startDev entry point (which is only used in Netlify Dev). When you're running a full build, I think the current information we print is useful, and if we feel that it isn't I think we should have a wider conversation to identify exactly what we want to show there.

[lukasholzer]

LGTM!