Ability to set labels for custom menus

[trojkat]

Original PR: helix-editor/helix#3958

[trojkat]

Already available in v0.1.1

Example

[keys.normal.space.f]
label = "File"
f = "file_picker"
s = { label = "Save", command = ":write" }
c = { label = "Edit config", command = ":config-open" }