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'
```

从 issue 中的安装命令开始，然后检查 google/cloud/aiplatform/tensorboard/uploader.py 和 logdir_loader.py，以追踪 TensorFlow 何时被导入。检查软件包依赖配置，并验证安装 tensorboard extra 后，所示的 TensorBoardUploader 导入不会出现 ModuleNotFoundError。

由索引模型根据 Issue 内容生成。