job manager: rename start_job callable to create_job

[soxofaan]

MultiBackendJobManager.run_jobs has a start_job callable to create a job and, as suggested by its name, to start it too.
However, blindly starting each job on creation is actually an anti-pattern with the job manager (which knows better when to start jobs, based on capacity).

We should rename start_job to create_job to make the better usage pattern more obvious

[soxofaan]

FYI I think we can do this rename while keeping start_job support for some time. We're already doing that with output_file

openeo-python-client/openeo/extra/job_management.py

Lines 450 to 457 in 7c321be

	if "output_file" in kwargs:
	if job_db is not None:
	raise ValueError("Only one of `output_file` and `job_db` should be provided")
	warnings.warn(
	"The `output_file` argument is deprecated. Use `job_db` instead.", DeprecationWarning, stacklevel=2
	)
	job_db = kwargs.pop("output_file")
	assert not kwargs, f"Unexpected keyword arguments: {kwargs!r}"