<!--

Welcome to Apache Airflow!  For a smooth issue process, try to answer the following questions.
Don't worry if they're not all applicable; just try to include what you can :-)

If you need to include code snippets or logs, please put them in fenced code
blocks.  If they're super-long, please use the details tag like
<details><summary>super-long log</summary> lots of stuff </details>

Please delete these comment blocks before submitting the issue.

-->

<!--

IMPORTANT!!!

PLEASE CHECK "SIMILAR TO X EXISTING ISSUES" OPTION IF VISIBLE
NEXT TO "SUBMIT NEW ISSUE" BUTTON!!!

PLEASE CHECK IF THIS ISSUE HAS BEEN REPORTED PREVIOUSLY USING SEARCH!!!

Please complete the next sections or the issue will be closed.
These questions are the first thing we need to know to understand the context.

-->

**Apache Airflow version**:


**Kubernetes version (if you are using kubernetes)** (use `kubectl version`):

**Environment**:

- **Cloud provider or hardware configuration**:
- **OS** (e.g. from /etc/os-release):
- **Kernel** (e.g. `uname -a`):
- **Install tools**: Docker

**What happened**:

When passing a templatized `dest_gcs` argument to the `S3ToGCSOperator` operator, the DAG fails to import because the constructor attempts to test the validity of the URL before the template has been populated in `execute`.

The error is:

```
Broken DAG: [/opt/airflow/dags/bad_gs_dag.py] Traceback (most recent call last):
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/providers/google/cloud/hooks/gcs.py", line 1051, in gcs_object_is_directory
    _, blob = _parse_gcs_url(bucket)
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/providers/google/cloud/hooks/gcs.py", line 1063, in _parse_gcs_url
    raise AirflowException('Please provide a bucket name')
airflow.exceptions.AirflowException: Please provide a bucket name
```

**What you expected to happen**:

The DAG should successfully parse when using a templatized `dest_gcs` value.

**How to reproduce it**:

Instantiating a `S3ToGCSOperator` task with `dest_gcs="{{ var.gcs_url }}"` fails. 

<details>

```python
from airflow.decorators import dag
from airflow.utils.dates import days_ago
from airflow.providers.google.cloud.transfers.s3_to_gcs import S3ToGCSOperator


@dag(
    schedule_interval=None,
    description="Demo S3-to-GS Bug",
    catchup=False,
    start_date=days_ago(1),
)
def demo_bug():

    S3ToGCSOperator(
        task_id="transfer_task",
        bucket="example_bucket",
        prefix="fake/prefix",
        dest_gcs="{{ var.gcs_url }}",
    )


demo_dag = demo_bug()
```
</details>


**Anything else we need to know**:

Should be fixable by moving the code that evaluates whether the URL is a folder to `execute()`.

airflow/providers/google/cloud/transfers/azure_fileshare_to_gcs.py
#
#
#
from tempfile import NamedTemporaryFile
from typing import Iterable, Optional, Sequence, Union
from airflow import AirflowException
from airflow.models import BaseOperator
from airflow.providers.google.cloud.hooks.gcs import GCSHook, _parse_gcs_url, gcs_object_is_directory
from airflow.providers.microsoft.azure.hooks.azure_fileshare import AzureFileShareHook
class AzureFileShareToGCSOperator(BaseOperator):
    """
    Synchronizes a Azure FileShare directory content (excluding subdirectories),
    possibly filtered by a prefix, with a Google Cloud Storage destination path.
    :param share_name: The Azure FileShare share where to find the objects. (templated)
    :type share_name: str
    :param directory_name: (Optional) Path to Azure FileShare directory which content is to be transferred.
        Defaults to root directory (templated)
    :type directory_name: str
    :param prefix: Prefix string which filters objects whose name begin with
        such prefix. (templated)
    :type prefix: str
    :param azure_fileshare_conn_id: The source WASB connection
    :type azure_fileshare_conn_id: str
    :param gcp_conn_id: (Optional) The connection ID used to connect to Google Cloud.
    :type gcp_conn_id: str
    :param dest_gcs: The destination Google Cloud Storage bucket and prefix