Expose programmatic equivalent of CLI commands

[araghukas]

What should we add?

For example:

from covalent_dispatcher import covalent_start, covalent_stop

# start covalent server from Python
covalent_start()

# stop covalent server from Python
covalent_stop()

These functions should consider pitfalls, like submitting a workflow immediately after starting covalent (i.e. the known missing dispatcher address error).

Describe alternatives you've considered.

This is doable using subprocess to issue "covalent start" or "covalent stop" shell commands.

[kessler-frost]

Implemented in #1854.