add an integration test with extension diretories as symlinks so that we can validate the version bump for commons-io

An extension loading issue was found when using commons-io version 2.9.0. In particular When the an extension directory is configured as a symlink, the symlink is not walked properly, and no jars are found, resulting in the extension not being loaded properly. An example of such a configuration for the druid-hdfs-storage extension is shown below:

```javascript
% pwd
/Users/user1/apache-druid-0.22.0-SNAPSHOT/extensions
%
% ls -al
total 0
drwxr-xr-x 29 user1 staff 928 Jun 29 12:38 .
drwxr-xr-x 12 user1 staff 384 Jun 29 12:35 ..
drwxr-xr-x 28 user1 staff 896 Jun 29 12:35 druid-avro-extensions
drwxr-xr-x 13 user1 staff 416 Jun 29 12:35 druid-aws-rds-extensions
drwxr-xr-x 10 user1 staff 320 Jun 29 12:35 druid-azure-extensions
drwxr-xr-x 3 user1 staff 96 Jun 29 12:35 druid-basic-security
drwxr-xr-x 5 user1 staff 160 Jun 29 12:35 druid-bloom-filter
drwxr-xr-x 4 user1 staff 128 Jun 29 12:35 druid-datasketches
drwxr-xr-x 3 user1 staff 96 Jun 29 12:35 druid-ec2-extensions
drwxr-xr-x 4 user1 staff 128 Jun 29 12:35 druid-google-extensions
lrwxr-xr-x 1 user1 staff 49 Jun 29 12:38 druid-hdfs-storage -> /Users/user1/druid-hdfs-storage
drwxr-xr-x 3 user1 staff 96 Jun 29 12:35 druid-histogram
drwxr-xr-x 10 user1 staff 320 Jun 29 12:35 druid-kafka-extraction-namespace
drwxr-xr-x 7 user1 staff 224 Jun 29 12:35 druid-kafka-indexing-service
drwxr-xr-x 11 user1 staff 352 Jun 29 12:35 druid-kerberos
drwxr-xr-x 6 user1 staff 192 Jun 29 12:35 druid-kinesis-indexing-service
drwxr-xr-x 38 user1 staff 1216 Jun 29 12:35 druid-kubernetes-extensions
drwxr-xr-x 5 user1 staff 160 Jun 29 12:35 druid-lookups-cached-global
drwxr-xr-x 7 user1 staff 224 Jun 29 12:35 druid-lookups-cached-single
drwxr-xr-x 20 user1 staff 640 Jun 29 12:35 druid-orc-extensions
drwxr-xr-x 15 user1 staff 480 Jun 29 12:35 druid-pac4j
drwxr-xr-x 24 user1 staff 768 Jun 29 12:35 druid-parquet-extensions
drwxr-xr-x 3 user1 staff 96 Jun 29 12:35 druid-protobuf-extensions
drwxr-xr-x 73 user1 staff 2336 Jun 29 12:35 druid-ranger-security
drwxr-xr-x 13 user1 staff 416 Jun 29 12:35 druid-s3-extensions
drwxr-xr-x 4 user1 staff 128 Jun 29 12:35 druid-stats
drwxr-xr-x 3 user1 staff 96 Jun 29 12:35 mysql-metadata-storage
drwxr-xr-x 4 user1 staff 128 Jun 29 12:35 postgresql-metadata-storage
drwxr-xr-x 3 user1 staff 96 Jun 29 12:35 simple-client-sslcontext
%
```

An issue was filed with the apache commons-io team https://issues.apache.org/jira/browse/IO-741.

We should add an integration test which tests this scenario so that we can bump the version of this dependency in the future with confidence.

Start by reproducing the configured extension-directory symlink scenario described in the issue, then locate the extension-loading integration-test entry point. Add coverage that walks the symlink, finds the extension JARs, and loads the extension successfully; the test should provide confidence when upgrading commons-io.

Written by the indexing model from the issue text.