Canvas: Allow more (custom) node and arrow shapes

[phl]

There is a related request here:

Canvas: Arrows of rectangular shape

Use case or problem I have a huge problem with a current shape of the arrows using Canvas plugin - I can’t connect nodes the way I want. For example: [2022-12-18_15-34-53] You can see this ugly bended arrow from Card D to the Card C, and also the arrow from A to B is also very weird. Proposed solution Just add ability to use rectangular arrows instead of curve ones. Here is how it looks in Miro with rectangular arrows: [2022-12-18_15-36-23] To save data about how exactly and where these …