public Builder addEnvironmentVariable(String name, String value) {
      environment.put(name, value);
      return this;
    }
Adds a variable in the container environment.

@param name the environment variable name
@param value the environment variable value
@return this
@see #setEnvironment
jib-build-plan/src/main/java/com/google/cloud/tools/jib/api/buildplan/ContainerBuildPlan.java