Document create_distributed_table_concurrently()

Currently, the documentation for the Citus API only includes create_distributed_table() and not create_distributed_table_concurrently[0]. The function in question is only documented in the README[1] and in a blog post[2].

We should document the function in the Citus API docs for better discoverability.

[0]: https://docs.citusdata.com/en/v13.0/develop/api_udf.html#create-distributed-table
[1]: https://github.com/citusdata/citus?tab=readme-ov-file#distributing-tables-without-interrupting-the-application
[2]: https://www.citusdata.com/blog/2022/09/19/citus-11-1-shards-postgres-tables-without-interruption/