[Feature] Loader supports more built-in datasets to load

### Search before asking

- [X] I had searched in the [feature](https://github.com/apache/incubator-hugegraph-toolchain/issues?q=is%3Aissue+label%3A%22Feature%22) and found no similar feature requirement.

### Feature Description (功能描述)

Now, there is one built-in dataset in loader. https://github.com/apache/incubator-hugegraph-toolchain/tree/master/hugegraph-loader/assembly/static/example/file
We can provide more built datasets to load.
There is the to-do list to realize the feature.
1. provide the download link of multi built-in datasets. (If the built-in datasets in the loader docker image or the compiled archive, the size of them will be very large)
2. A shell to download and unzip the dataset.
3. Related doc and README.

### Are you willing to submit a PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

Start by inspecting hugegraph-loader/assembly/static/example/file and the loader's packaging for the existing built-in dataset. Define download links for additional datasets, provide a shell workflow that downloads and unzips them, and update the related documentation and README. Done means the datasets can be obtained and loaded through the documented workflow without enlarging the loader archive or Docker image.

Written by the indexing model from the issue text.