**Description**
The Airflow logs generated by the Livy operator currently only state the status of the submitted batch. To view the logs from the job itself, one must go separately to the session logs. I think that Airflow should have the option (possibly on by default) that retrieves the session logs after the batch reaches a terminal state if a `polling_interval` has been set.

**Use case / motivation**
When debugging a task submitted via Livy, the session logs are the first place to check. For most other tasks, including SparkSubmitOperator, viewing the first-check logs can be done in the Airflow UI, but for Livy you must go externally or write a separate task to retrieve them. 

**Are you willing to submit a PR?**

I don't yet have a good sense of how challenging this will be to set up and test. I can try but if anyone else wants to go for it, don't let my attempt stop you.

**Related Issues**

None I could find

airflow/providers/apache/livy/hooks/livy.py
body['className'] = class_name
        if args and LivyHook._validate_list_of_stringables(args):
            body['args'] = [str(val) for val in args]
        if jars and LivyHook._validate_list_of_stringables(jars):
            body['jars'] = jars
        if py_files and LivyHook._validate_list_of_stringables(py_files):
            body['pyFiles'] = py_files
        if files and LivyHook._validate_list_of_stringables(files):
            body['files'] = files
        if driver_memory and LivyHook._validate_size_format(driver_memory):
            body['driverMemory'] = driver_memory
        if driver_cores:
            body['driverCores'] = driver_cores
        if executor_memory and LivyHook._validate_size_format(executor_memory):
            body['executorMemory'] = executor_memory
        if executor_cores:
            body['executorCores'] = executor_cores
        if num_executors:
            body['numExecutors'] = num_executors
        if archives and LivyHook._validate_list_of_stringables(archives):
            body['archives'] = archives
        if queue:
            body['queue'] = queue
        if name:
            body['name'] = name
        if conf and LivyHook._validate_extra_conf(conf):
            body['conf'] = conf
        return body
    @staticmethod
    def _validate_size_format(size: str) -> bool: