[docs] <rh-alert> toast design specifications

[zeroedin]

Description

While helping an implementor with rh-alert and toast, I noted that the specifications on the styles tab were a bit vague and lacked explanation.

We need to add the spacerTokenTable as well as descriptors for each image under Spacing.

https://ux.redhat.com/elements/alert/style/#space

Screenshots

No response

Steps to reproduce

1. Go to https://ux.redhat.com/elements/alert/style/#space

Expected behaviour

Note missing info.

Operating System (OS)

iOS, macOS, Linux, Windows

Browser

Chrome, Safari, Safari iOS, Microsoft Edge, Firefox

Additional browser or assistive technology info

No response