knot: add functional test.sh covering all CLI subpackages

knot: add functional test.sh covering all CLI subpackages

Cover each user-facing subpackage with a real functional check instead
of relying solely on the CI's generic --version probe:

- knot:           knotc conf-check on a minimal YAML server config
- knot-dig:       kdig -h (CLI parser smoke check)
- knot-host:      khost -h
- knot-nsupdate:  feed 'quit' through the REPL
- knot-zonecheck: validate a minimal example.com zone file end to end
- knot-keymgr:    initialise a KASP DB in a temp directory

knot-libs, knot-libzscanner, and knot-tests are library/harness
subpackages; the generic ELF/SONAME checks already cover them.

Signed-off-by: Alexandru Ardelean <redacted>