describegpt: add a --jsonl option to save results to a jsonl, if the file exists, add the result to it

[jqnatividad]

So users can persist the results.

Apart from the standard results, the jsonl file should also include the timestamp and the name of the --prompt-file used (#1085 ).

[jqnatividad]

#1106 sets the stage for this

[rzmk]

@jqnatividad What would be an expected output for this command?

For example printed on terminal and potentially a file if using --prompt-file, --output, & --all:

{"prompt_file": {"name": "demo.json", "timestamp": "1996-12-19T16:39:57-08:00"}}
{"dictionary": "..."}
{"description": "..."}
{"tags": "..."}

Also if --json is also used should we replace the plaintext "..." output with the JSON output {...}?

[jqnatividad]

@rzmk , the resulting output should read as valid json-lines (https://jsonlines.org/).

With each jsonl record having the following structure. Here are two pretty-printed json records for readability:

[
   {
      "prompt_file": "demo.json",
      "timestamp": "1996-12-19T16:39:57-08:00",
      "dictionary": "...",
      "description": "...",
      "tags": "..."
   },
   {
      "prompt_file": "demo.json",
      "timestamp": "1996-12-20T16:39:57-08:00",
      "dictionary": "...2",
      "description": "...2",
      "tags": "...2"
   }
]

But it should actually look like this, as jsonl calls for each record being separated by a newline:

{"prompt_file":"demo.json","timestamp":"1996-12-19T16:39:57-08:00","dictionary":"...","description":"...","tags":"..."}
{"prompt_file":"demo.json","timestamp":"1996-12-20T16:39:57-08:00","dictionary":"...2","description":"...2","tags":"...2"}