imgtool: Output format option to dumpinfo

[5frank]

Add option -F, --format [yaml|json|human] to imgtool dumpinfo command.

Backward compatible:

• imgtool dumpinfo input.bin --> human-friendly format to stdout (default)
• imgtool dumpinfo --outfile=output.txt input.bin --> YAML format to file (existing behavior)
• imgtool dumpinfo --format=json input.bin --> JSON format to stdout
• imgtool dumpinfo --format=yaml input.bin --> YAML format to stdout

JSON output has both "type" and "type_name", example:
"tlvs": [ { "type": 16, "type_name": "SHA256", ... } ]

[nordicjm]

@fundakol please review

[nordicjm]

@5frank please see failing CI

[fundakol]

Usage of dumpinfo is now very confusing.

• this command does nothing: imgtool dumpinfo zephyr.signed.bin --format human -o dump.txt --silent
• this command: imgtool dumpinfo zephyr.signed.bin --format human -o dump.txt works same as imgtool dumpinfo zephyr.signed.bin and imgtool dumpinfo zephyr.signed.bin --format yaml
• when human format is selected option outfile has no effect

imgtool dumpinfo zephyr.signed.bin --format yaml -o dump.yaml --> produced different yaml then it was before your change, so it is not backward compatible.