Add "following" TweetReplySetting enum

[ConnorSinnott]

While not documented on Twitter's Object Model, "following" is a new value being returned by reply_settings.

[IDs and names obfuscated]

        {
            "id": "1445555554710916097",
            "reply_settings": "everyone",
            "text": "@WhereWhereJoeJoes We're so happy to have you as a member of our community 🥰"
        },
        {
            "id": "144555555545356289",
            "reply_settings": "following", <==== New?
            "text": "@mooretyyy We love it 😍"
        },
        {
            "id": "1455555555229575682",
            "reply_settings": "everyone",
            "text": "@cdgelodge @caracaradd Shout out to the mountain for being a sponsor 😂⛰️❤️"
        },

[ConnorSinnott]

Hey @DanielaSfregola! I've got a small adjustment ready for you. This value is being returned from their API but isn't listed on the docs.