Add Karla font family to Material UI theme

[henryk1229]

Is your feature request related to a problem? Please describe.
While working on #1641, @kennyycheng requested that the components use the Karla font - this is an easy change, but since it would effect every component that consumes our material ui theme, we decided the change merited a separate issue + pr (#1641 (comment))

Describe the solution you'd like
the createMuiThemeV1 function in mui-theme.ts should be updated to include a typography field, with sub-field fontFamily: 'Karla', so that the font is included in the theme.

Describe alternatives you've considered
n/a

Additional context
n/a