[Feat][Doc] Generate GAR files of whole `ldbc-sample` property graph as an example to demonstrate GAR format

**Is your feature request related to a problem? Please describe.**
Maybe we need a widely-used property graph to demonstrate the GAR file format. The ldbc dataset seems to be a good choice.

This issue can be a `good first issue` for a developer.

**Describe the solution you'd like**
Generate formatted files in GraphAr for a property graph including:
- [ ] design the metadata files (in Yaml) for the ldbc graph, the file format of chunk files can be `csv` for easy to read
- [ ] generate GAR data files with the Spark library
- [ ] add some tests to check the data files are match to the metadata information through utilizing the Info classes

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
related to issue #37

Start by reviewing the ldbc-sample graph and related issue #37, then locate the project’s metadata and Info-class entry points. Define YAML metadata and readable CSV chunks, generate the GAR data with Spark, and add checks that the data matches the metadata; done means the example files and tests are complete.

Written by the indexing model from the issue text.