fix: usr: dig +yaml producing invalid YAML when a lookup fails

When "dig +yaml" was run and no server could be reached, dig printed its plain-text startup banner (the "; \<\<\>\> DiG ..." and ";; global options" lines) ahead of the machine-readable output, so the result was not valid YAML and could not be parsed. dig no longer emits that banner in YAML mode. As part of the same change, the banner is now built only after the whole command line has been read, so options given after the query name (such as +nocmd, +short and +yaml) are correctly reflected in it.

Closes #1230

Merge branch '1230-dig-fix-error-comments' into 'main'

See merge request isc-projects/bind9!12416