Reloading the config at runtime

[jaeheonji]

This Feature organizes tasks for the end goal of allowing users to modify and reload zellij configuration files at runtime.

The following features are subsets of this feature and must be included in implementation:

• Configure keybindings at runtime #1405
• Theme change detection during runtime #2249
• [Feature Request] Allow keybindings to change configuration options #2645

This also requires distinguishing whether each option allows changes at runtime. For example, It is difficult to apply ​​to options such as default_mode or mirror_session when reloading. Instead, I think we can handle like UI related options such as simplified_ui or pane_frames

[jaeheonji]

#3422

This PR will help to implement this feature.