Option to display RAM in GB/MB instead of % on the panel

### Problem

Hi! Your app fits elementary OS perfectly.

I have a suggestion: please add an option to display the actual amount of RAM used (e.g., 2.8 GB) on the wingpanel indicator instead of just the percentage.

For many users, 75% usage looks alarming (even if it's just cache), while seeing absolute values like "2.8 GB" provides much better clarity.

Thanks for your great work!

### Proposal

Add a toggle or an option in the settings to switch between "Percentage" and "Absolute values" (GB/MB) for the RAM indicator on the wingpanel.

### Prior Art (Optional)

_No response_