I'm actually one of those people who is naturally friendly and amiable. My mom says I woke up with a smile on my face and rarely cried as a baby. She described me as a boring baby. When I walked into a room, I would change the mood. I don't quite have the same effect as an adult, but I do know that I can usually calm irate people when I've worked in customer service. I don't hold resentment, because I know we all make mistakes. We all are going to hurt someone else at some point.
My daughter is also naturally charming and people are drawn to her. She can make the grumpiest person smile.When she wakes up, she is sunshiny and loving.
Honestly, I think you are born with the right genes. I also think you are raised with appreciative parents who valued your natural gifts, so you learned to appreciate your own. The more happy you are with yourself, the easier it is to express friendliness to others. Plus, there is a certain amount of faking it. There are days when I feel lousy, feel like the world could just crash in on me, but as soon as I see another human being, a smile is planted on my face, and a pleasant tone in my voice. Sometimes my ability to fake it surprises me. It's actually an unconscious habit I have.
There are drawbacks to this type of personality. You can get used, you also attract depressed people. People feel compelled to tell you their life problems. It's semi-amusing in a way. My husband often grins at me when he notices a random person has attached themselves to me telling me their life problems.