Allow using different graphviz engines

[meshuga]

The tool currently uses dot engine to visualise the diagrams. That tool is good for hierarchical, small graphs. With bigger diagrams, the engine starts showing its suboptimality.

In https://github.com/Cloud-Architects/aws-network-discovery, we discovered sfdp engine to work well with bigger diagrams but right now the engine is passed to diagrams in a hacky way - https://github.com/Cloud-Architects/aws-network-discovery/blob/2b6c555886cdcd4517b6da13bc41b8d0fdb1ab7a/shared/diagram.py#L171.

It would be good for the tool to provide a configuration, to be able to select graphviz engine.

[clayms]

@meshuga - totally agree.

You can use different Graphviz engines. Just set the graph_attr "layout" parameter to "neato" or "fdp".

See these answers:
#17 (comment)
#243 (comment)
#279 (comment)

[meshuga]

@clayms Thanks for the response. For the tool I develop I found sfdp most useful as it can render complex network diagrams, other engines have troubles in doing so and the way it is done uses non-documented and potentially breaking internal features - https://github.com/Cloud-Architects/cloudiscovery/blob/v2.2.4/cloudiscovery/shared/diagram.py#L297

The thing that bothers me is fact that there's no support of the regular clusters, something e.g. diagrams.net has. Becasue of that, I started work to move parts of the diagrams (AWS VPC diagram generation away from this library, in favour of diagrams.net) - Cloud-Architects/cloudiscovery#158 (comment)

Generated sample below gives a proof it's not something impossible:

FYI @leandrodamascena