Enable deep sleep and add wakeup-source property

[koshelevdk]

This change is to decrease power consumption of keyboard.

• CONFIG_ZMK_SLEEP enables deep sleep support.
• wakeup-source; property to be able to wake up from sleep.

Issue #1

[koshelevdk]

Not building without disabling rgb.

[awkannan]

To have RGB work it seems we need the same fix as this PR here:
zmkfirmware/zmk#2424

I'll pull in the fixes, test, and then push this.

[awkannan]

I will need a little extra time to test, but in the meantime, you can try this PR:
#3

[koshelevdk]

Thank you @awkannan. I don't have this specific problem, because i've disabled rgb in my main branch.
That's the main reason why I pushed PR without additional checks. Only later realized that it's not building.

[koshelevdk]

Closed in favor of #3