Add flag --aio or --all to the start command

[DenuxPlays]

Feature Request

Is your feature request related to a problem? Please describe.

Currently when I want to distribute my application via Docker I need to host two services because it is not possible to run the server, worker and scheduler in one process.

Also someone else asked about this:
#1198 (comment)
This is also where I noticed I would benefit from the feature.

IMO the big point is that both the end-user and developer would benefit from this feature.
Easier deployment for the end-user and easier development as everything can be started with one command.

Describe the solution you'd like

Currently there is a flag to start the server and worker ( --server-and-worker) I would introduce something similar for the scheduler.

But maybe we could replace this flag with something like (--components=server,worker,scheduler) to keep it modular?
This could also be done without any breaking changes. Just dont remove the old flag and deprecate it.

The easiest way would of course be a --all flag and I do not think there is a use case where you want to start the server and scheduler but not the worker, but maybe I am wrong there.

Describe alternatives you've considered

In docker you could run two services managed by supervisord.
This isn't optimal and not very "dockerly" but it would work.

Contribution

Again if this is wanted and we can agree to a solution I am open to contribute.

[jondot]

I think we can work this according to frequency of use. Let's build some logic foundations:

1. The "correct" way is to use a different process to run and keep running the different aspects: worker, server, scheduler
2. In accordance to our "simplify" mantra, we currently provide: server+worker, but keep the scheduler separate
3. Due to user requests for more simplification we can expand (2) to include the scheduler

I think here being explicit is better than --all, because --all does not say what is going to be run today, nor what will run in the future (will we have more runner processes? more kinds of workflows?).

(1)

cargo loco start --server-and-worker --scheduler

To create symmetry we can do

(2)

cargo loco start --server --worker --scheduler

You can submit a PR for any of (1) or (2).
In case of (2) we'd like to preserve the --server-and-worker flag for backwards compat.

Please note that running (or coordinating) the different processes may be tricky (you need to run a main process and then spin off N threads and join on them), so apply special attention in the code block that coordinates and run these.