Custom Partitioning: Erase and install button label is ambiguous

### What Happened?

After setting up custom partitions and selecting from amongst several others on the disk those desired for the `boot-efi`, `root` and `swap` partitions. The "Erase and Install" button became active. It took a certain act of faith to press this button as it is not explicit exactly what will be erased. Although in the "Custom Partition" dialog, elementaryos has an option to erase the whole disk and there was some concern that this might happen.

### Steps to Reproduce

Set up custom partitions for `boot-efi`, `root` and `swap`
Observe the "Erase and Install" button

### Expected Behavior

The button should be labelled in a way that confirms that **only** the selected partitions will be erased.

### OS Version

7.x (Horus)

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

_No response_