Include `grace` in LinearScaleOptions type definition (#8847)

This commit adds the `grace` option, to the LinearScaleOptions type definition
as documented here,
https://www.chartjs.org/docs/latest/axes/cartesian/linear.html#grace. Without
this commit the TS compiler does not allow the option.

Signed-off-by: Moses Mendoza <mendoza.moses@gmail.com>