ICSHWI-11855: Login button has border on deploy-fe but not on template-fe

Updates the Login and ButtonAppBar stories with examples of using the login button with an outlined variant instead.

Of note, the outlined variant in particular uses the primary color instead of the contrast text color; this means that when used on e.g. the ButtonAppBar you need to specify the color as the contrastText instead.

A custom color was added to the palette as an example of doing this (appending the custom color after the custom theme was instantiated, so we could e.g. simply reference theme.palette.primary.constrastText dynamically instead of hard-coding it inline.