Add "safe" alternatives for creation functions

[richierocks]

The API allows you to create projects and tasks with the same name as existing projects/tasks.

It would be useful to have safe alternatives that check if the thing already exists, and only create it if it doesn't.

For example, a safe version of asn_projects_create_in_team() could look like this.

asn_safe_projects_create_in_team <- function(team, name, ..., options = list()) {
  project <- asn_projects_find_by_team(team = team) %>% 
    filter(name == !!name)
  
  if(nrow(project) > 0) {
    warning(sprintf("A project with name %s already exists.", name))
    project_id <- get_gid(project)[[1]]
    return(asn_projects_find_by_id(project_id))
  }
  
  asn_projects_create_in_team(team = team, name = name, ..., options)
}

The use case I'm thinking about is that I want to have an airflow task that pulls data on exercise issues each day, and add them to a project. Since most of the tasks will already exist from the previous day, I want to check whether or not it already exists before creating it.

I think that this sort of safe checking is a common enough pattern that it ought to exist here. If not, I can put it in dcasana instead.

cc: @ramnathv