docs(misconf): Improve documentation for filtering

[simar7]

Improving documentation around filtering

1. If the documentation were updated to discuss this issue in an easily-discovered form - right now you're fighting years of stale information on Google / Stack Exchange / etc. and there isn't a top-level ignore topic in the documentation search. One thing which might be useful would be expanding the paragraph at the top of https://aquasecurity.github.io/trivy/v0.46/docs/configuration/filtering/ to have some of the common search keywords like “ignore”, “suppress”, or “false-positive”.

Suggestion: Maybe we can add some keywords in the pages to help us better SEO

2. There is a low-context search hit on .trivyignore.yaml which is almost what you want except that it doesn't have much context or intro (this would help when looking at the documentation search results) and it needs to lead with the warning that this isn't enabled by default and has to be explicitly enabled on the command-line. I think it'd make sense to enable it by default on the grounds that in the unlikely event someone has created a conflicting file for another purpose, they'd want to know about it sooner rather than later.

3. The inline comment support is documented but it doesn't show up in the documentation search so it's easy to miss at the bottom of the page.

Originally posted by @acdha in #2961 (comment)