Let $f : ( 0,2 ) \rightarrow R$ be defined as $f ( x ) = \log _ { 2 } \left( 1 + \tan \left( \frac { \pi x } { 4 } \right) \right)$.\\
Then, $\lim _ { n \rightarrow \infty } \frac { 2 } { n } \left( f \left( \frac { 1 } { n } \right) + f \left( \frac { 2 } { n } \right) + \ldots + f ( 1 ) \right)$ is equal to $\_\_\_\_$.