[New sample] S3 Browser extension install

The [jupyterlab-s3-browser](https://github.com/IBM/jupyterlab-s3-browser) extension is useful for browsing Amazon S3 buckets and objects from within the SageMaker Studio UI - and was one of the tools specifically called out in the [Studio JupyterLab v3 launch blog](https://aws.amazon.com/blogs/machine-learning/amazon-sagemaker-studio-and-sagemaker-notebook-instance-now-come-with-jupyterlab-3-notebooks-to-boost-developer-productivity/).

S3 Browser was originally drafted for inclusion alongside LSP-related features (also mentioned in the blog) in #14 - but review requested it be separated out. Raising this issue to track the ask.

The extension is not particularly challenging to install in JLv3 (`pip install jupyterlab-s3-browser`), but can cause pip to overwrite default installed botocore/aiobotocore versions which could have unintended, adverse consequences.

I've been working around that with a script something like:

```bash
# Since pip can sometimes fail to take all installed packages into account, we'll look up and
# specify the current botocore/boto3 versions to avoid pip breaking things:
BOTO3_VER=`pip show boto3 | grep 'Version:' | sed 's/Version: //'`
BOTOCORE_VER=`pip show botocore | grep 'Version:' | sed 's/Version: //'`

pip install jupyterlab-s3-browser \
boto3==$BOTO3_VER \
botocore==$BOTOCORE_VER
```

Was hoping to draft something quickly for this to work in both JLv3 and JLv1 (since early versions of the extension appear to pre-date even JLv2), but have been struggling to try and get the installation working properly on SMStudio JLv1.

No target file or test is named. Start by testing the documented `pip install jupyterlab-s3-browser` flow and the shown boto3/botocore version-pinning script in SageMaker Studio JupyterLab v1 and v3; done means a lifecycle-config sample installs the extension without breaking the existing AWS package versions in both environments.

Written by the indexing model from the issue text.