Report errors directly to the user and document

[wagoodman]

What would you like to be added:

• grype should return 1 when running into fatal HTTP return codes (e.g. 429 and 5xx). This definition could be expanded as we find more cases.
• A new errors section in the JSON document that highlights both fatal and non-fatal but notable issues that arise during matching (e.g. http 404)
• Summarize any errors to the table output as an addendum
• Consider adding a new flag or config option to ignore any typically-fatal errors and allow grype to continue and return 0 in those cases

Why is this needed:
Today any errors get silently logged, but could affect the report results, which is not good (#2384 for example). Transient issues that lead to different results should always be presented to the user both in the UI and in the document (when the requested format supports doing so).