Make a function to schedule messages

[reharri7]

https://api.slack.com/messaging/scheduling

Going to use this to schedule announcements

[jsontm]

You can use Slack-morphism for this, method is here: https://github.com/abdolence/slack-morphism-rust/blob/master/src/api/chat.rs#L103

Request structure is as follows:

pub struct SlackApiChatScheduleMessageRequest {
    pub channel: SlackChannelId,
    pub content: SlackMessageContent,
    pub post_at: SlackDateTime,
    pub as_user: Option<bool>,
    pub icon_emoji: Option<String>,
    pub icon_url: Option<String>,
    pub link_names: Option<bool>,
    pub parse: Option<String>,
    pub thread_ts: Option<SlackTs>,
    pub username: Option<String>,
    pub reply_broadcast: Option<bool>,
    pub unfurl_links: Option<bool>,
    pub unfurl_media: Option<bool>,
}