[Task]: (DOC) improve yamlinput.adoc

### What needs to happen?

Migration: https://issues.apache.org/jira/browse/HOP-4043

https://hop.apache.org/manual/next/pipeline/transforms/yamlinput.html needs clarifications:

- What kinds of YAML files can it read? Can they be nested to many levels? How are "rows" formed from the input, i.e. when is a new row started?
- "get source from a field" and "Filename fieldname": looking at the description, these two are the same. Even if not, put them side by side (in the FILE TAB) and clarify what's the difference
- FILE TAB: indent some rows to show the nesting ([HOP-4041](https://issues.apache.org/jira/browse/HOP-4041))
- "Limit: Sets a limit to be read": what is this, number of files? Number of lines? Lines per file?
- "Add files to result filesname": what's this? Add description. The name has a typo (needs a space)
- "Key: The key to the element.": what's this and how is it different from "Name: The name of the output field."
- "Trim type: The type of trimming to use": what trim types there are?
- "Get fields: Approximates fields from the input": ok, this reads the YAML to find what fields it includes. But if I don't use it and specify wrong options (eg key="foo" where "foo" doesn't appear in YAML) or conflicting options (eg type="Integer" for a field that's alphabetic), what happens?

### Issue Priority

Priority: 3

### Issue Component

Component: Documentation

Start with the YAML Input manual page linked in the issue and investigate the transform behavior behind each listed question, including file nesting, row formation, limits, fields, trimming, and result filenames. Update the page so every bullet is answered, the FILE tab nesting and wording are clear, and the typo is corrected.

Written by the indexing model from the issue text.