feature: collapsible sidenav groups

[leetheman]

Hello, is it possible to have a property to set the default state for SiedNav collapsible groups, I have a very large sidenav and I don't want all the options to be open.

If possible, it would be great if there were two types of collapsible - normal style (each group can be collapsed /expended indepdenently) or accordian (expanding a group will close all others)

Happy to assist in the dev of this if that's an option?

[karan-kang]

Thanks for your feedback @leetheman, I will add this is upcoming release