Merge branch 'feat/3971_compact_json_and_jsonl_support' of https://github.com/echoech...

Merge branch 'feat/3971_compact_json_and_jsonl_support' of https://github.com/echoechoin/util-linux

* 'feat/3971_compact_json_and_jsonl_support' of https://github.com/echoechoin/util-linux:
  jsonwrt: simplify ul_jsonwrt_empty() and add comments for COMPACT format
  column: using switch-case replaces if-else
  column: add JSON compact format output subtest.
  column: add JSON LINES format output subtest.
  column: introduce LIBSMARTCOLS_JSON environment argument
  jsonwrt: support Compact JSON format output
  libsmartcols: support JSON Lines format output