ref: document `dvc queue` and `dvc exp` task-queuing changes

Docs meta-issue for https://github.com/iterative/dvc/issues/7592

• Initial documentation (command refs) will be driven by the core team.
• Update existing exp commands/flags that get aliased/deprecated or otherwise chaged.
• User guides/ other docs should be updated, but existing functionality is being preserved (so there is no special rush on this rn).

[karajan1001]

I understand that by default this goes into a background process. Is there a way to start it in the foreground? Say queue start --attached

There is currently no flag for this. In the meantime you can use exp run --run-all to get the same behavior, but eventually this can be folded into a flag for queue start

queue logs -f/--follow without a task should automatically follow the currently running experiment in the future.

Please confirm the difference or overlap between this and exp remove.

When developing the queue related feature. What I realized is that queue tasks and experiment are different aspects. Although they are strongly related but are still different. tasks are more focused on execution while experiments are more focused on the result. One checkpoint task can generate dozens of experiments, and experiments can be run without using a queue worker. The difference also comes into the status/show table, we can delete a succeeded task msg and leave the experiment result (revision) untouched.

[dberenbaum]

I think we can at least start with the current help output to give an overview:

$ dvc queue --help
usage: dvc queue [-h] [-q | -v] {start,stop,status,logs,remove,kill} ...

Commands to manage experiments queue.
Documentation: <https://man.dvc.org/queue>

positional arguments:
  {start,stop,status,logs,remove,kill}
                        Use `dvc queue CMD --help` to display command-specific help.
    start               Start experiments queue workers.
    stop                Stop experiments queue workers.
    status              List the status of the queue tasks and workers.
    logs                Show output logs for a task in the experiments queue.
    remove              Remove tasks in experiments queue.
    kill                Kill tasks in experiments queue.

optional arguments:
  -h, --help            show this help message and exit
  -q, --quiet           Be quiet.
  -v, --verbose         Be verbose.