add keepabove window rule

[TRPB]

I've been trying to control the Z-order of various UI elements. In particular, I've been trying to get Waybar to appear over wf-dock.

This allows setting up a window rule as such:

rule_1 = on created if app_id is "waybar" then keepabove

This isn't quite the same as the shortcut key as it sets wf::LAYER_TOP to force the window to the top. The keypress which targets workspace windows sets wf::WORKSPACE and SUBLAYER_DOCKED_ABOVE.

This might need a different name? E.g.

rule_1 = on created if app_id is "waybar" then toppanel # uipanel  depanel or whatever

[TRPB]

just a thought, would it be better going forward to support something like:

on created if app_id is "....." then layer top above
on created if app_id is "....." then layer workspace above
on created if app_id is "....." then layer top below
on created if app_id is "....." then layer background above

it would add more flexibility for customisation, things such as desktop widgets and the like.

[ammen99]

Just realized this feature is available on master since quite some time, nonetheless thanks for sending this PR!