remove graphviz-rust dependency

[milenkovicm]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

I suggest to make graphviz-rust dependency optiona, and move rendering of execution graphs from scheduler to a UI library. In order to use graphviz-rust a graphviz has to be installed on local server, we can eliminate this dependency.

UI can use libraries such as https://github.com/dagrejs/graphlib-dot and /api/job/:job_id/dot to render dot definitions as svg.

Describe the solution you'd like

• Make graphviz-rust optional, disabled by default (/api/job/:job_id/dot_svg) .

Describe alternatives you've considered

Additional context