add_experiment_if_not_exists: Add experiment if not exists
In mljar/mljar-api-R: R API for MLJAR

Check if experiment exists, verifies parameters, creates data to create_experiment function and finally starts creation of MLJAR experiment.

add_experiment_if_not_exists(project_hid, train_dataset, valid_dataset,
  experiment_title, project_task, validation_kfolds, validation_shuffle,
  validation_stratify, validation_train_split, algorithms, metric, tuning_mode,
  time_constraint, create_ensemble)

`project_hid`	character with project identifier
`train_dataset`	character with path to training dataset
`valid_dataset`	character with path to validation dataset
`experiment_title`	character with experiment title
`project_task`	character with project task
`validation_kfolds`	number of folds to be used in validation
`validation_shuffle`	boolean which specify if shuffle samples before training
`validation_stratify`	boolean which decides whether samples will be divided into folds with the same class distribution
`validation_train_split`	ratio how to split training dataset into train and validation
`algorithms`	list of algorithms to use
`metric`	charcater with metric
`tuning_mode`	tuning mode
`time_constraint`	numeric with time limit to calculate algorithm
`create_ensemble`	whether or not to create ensemble