Lower refresh rate while not used to save energy

[nailgun]

Is your feature request related to a problem? Please describe.
I like to keep k9s running in a dedicated terminal window all the time. However, due to constant screen refreshes, it consumes a significant amount of laptop battery.

Describe the solution you'd like
It would be great if k9s could refresh less frequently when the terminal window is not focused. I see two possible ways to achieve this:

1. Use the focus reporting extension of the ECMA-48 standard, defined and popularized by Xterm and became a de facto standard in many modern terminal emulators.
   The application can request focus reporting by sending the escape sequence ESC [ ?1004h.
   The terminal will then send back ESC [ I when the window gains focus and ESC [ O when it loses focus.
   To disable reporting, the application sends ESC [ ?1004l.
   k9s could use these signals to dynamically adjust its refresh rate.

2. Alternatively, the refresh rate could be reduced after a certain period of user inactivity (no input detected).

Describe alternatives you've considered
I’ve checked if iTerm2 or tmux provide a built-in way to suspend an application or pause its output when unfocused, but didn’t find any equivalent feature.