tfdbg: add persistent config

* Add two persistent UI configurations backed by a file at ~/.tfdbg_config by default.
  * graph_recursion_depth, which controls the recursive output of li/lo commands.
  * mouse_mode, which controls the mouse state of the CursesUI.
* Add `config` command to set and inspect the persistent configuration. E.g.,
  * config show
  * config set graph_recursion_depth 3
  * config set mouse_mode False

Fixes: #13449
PiperOrigin-RevId: 172270804