Add possibility to reorder server groups

[KeterSCP]

Describe the solution you'd like

Nowadays, after adding new server group in the object explorer there is no way to change its display order. It would be nice to have something like a drag-and-drop functionality to reorder list items.

Describe alternatives you've considered

Alternatively, server groups could be sorted in alphabetical order. Currently, only newly added server groups are placed alphabetically, but renaming existing ones does not rearrange the structure. (UPD: it does rearrange the structure, but only after using View->Reload option or restarting the whole pgadmin app)

[pravesh-sharma]

We need to sort the server groups alphabetically when adding or renaming. Looks like a bug.