Function issues_slash_add_labels 

pub async fn issues_slash_add_labels(
    configuration: &Configuration,
    owner: &str,
    repo: &str,
    issue_number: i32,
    issues_add_labels_request: Option<IssuesAddLabelsRequest>,
) -> Result<Vec<Label>, Error<IssuesSlashAddLabelsError>>

Adds labels to an issue. If you provide an empty array of labels, all labels are removed from the issue.