Enable efficiency mode to reduce battery usage

**Is your feature request related to a problem? Please describe.**

I noticed a small but measurable increase in power usage when not plugged-in after using Flow Launcher for a few weeks or so. Manually setting "Efficiency mode" to the flow launcher executable in Task Manager solves this.

**Describe the solution you'd like**

For Flow Launcher to automatically set itself on efficiency mode on start up.

**Describe alternatives you've considered**

Manually set Flow Launcher to efficiency mode every restart.

**Additional context**
Firefox implementation: https://github.com/mozilla/gecko-dev/blob/30dfc0e2fcfec889f94fbd0ec5f20822c276c0fb/hal/windows/WindowsProcessPriority.cpp

Windows API reference: https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-setprocessinformation