fix(ui): Fix incorrect default value setting OR operator when parsing React configs

[deadlycoconuts]

Context

The OR operator used to set default values for REACT_APP_ALLOW_CUSTOM_STREAM and REACT_APP_ALLOW_CUSTOM_TEAM is incorrect.

Example:
What we want is when REACT_APP_ALLOW_CUSTOM_STREAM is defined, return the value of REACT_APP_ALLOW_CUSTOM_STREAM, otherwise return true. However, when REACT_APP_ALLOW_CUSTOM_STREAM is false:

getEnv("REACT_APP_ALLOW_CUSTOM_STREAM") || true 
is equals to false || true 
is equals to true

which is incorrect.

This PR fixes this by replacing the OR operator with a ternary operator to check if the environment variable is defined or not, and returns that value if it is, and returns true if it isn't:

getEnv("REACT_APP_ALLOW_CUSTOM_STREAM") != null
      ? getEnv("REACT_APP_ALLOW_CUSTOM_STREAM")
      : true