Missing tensorflow dependency

#### Environment details

- OS type and version: macOS Sequoia 15.6
- Python version: 3.10
- pip version: 24.3.1
- `google-cloud-aiplatform` version: 1.108.0

#### Steps to reproduce

1. `pip install "google-cloud-aiplatform[tensorboard]==1.108.0"`
2. `python -c "from google.cloud.aiplatform.tensorboard.uploader import TensorBoardUploader"`

The following error will appear:
```
ModuleNotFoundError: No module named 'tensorflow'
```

#### Code example

See above.

#### Stack trace
```
Traceback (most recent call last):
File "", line 1, in
File "/Users/.../.pyenv/versions/.../lib/python3.10/site-packages/google/cloud/aiplatform/tensorboard/uploader.py", line 41, in
from google.cloud.aiplatform.tensorboard import logdir_loader
File "/Users/.../.pyenv/versions/.../lib/python3.10/site-packages/google/cloud/aiplatform/tensorboard/logdir_loader.py", line 22, in
import tensorflow as tf
ModuleNotFoundError: No module named 'tensorflow'
```

Start with the installation command in the issue, then inspect google/cloud/aiplatform/tensorboard/uploader.py and logdir_loader.py to trace when TensorFlow is imported. Check the package dependency configuration and verify that installing the tensorboard extra allows the shown TensorBoardUploader import without ModuleNotFoundError.

Written by the indexing model from the issue text.