refact: Add lowercase conversion for keycodes

[jeevithakannan2]

Type of Change

• [x] Refactoring

Description

• Convert the keys to lowercase eliminating the need to specify both the capital and non-capital keycodes for a specific action.
• Keys that don't need to be converted to lowercase for example theme switching can be declared in the KEYS_NOT_TO_NORMALIZE
• Renamed function toggle_task_list_guide to enable_action_guide for consistency

Testing

• Works as expected no issues.

Checklist

• [x] My code adheres to the coding and style guidelines of the project.
• [x] I have performed a self-review of my own code.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] My changes generate no errors/warnings/merge conflicts.