Show DuckDB version in a file

[szarnyasg]

The repository should contain the corresponding DuckDB version in a file.

Currently, it can be retrieved via using the submodule if one looks up the Git tags but this is not ideal.

[ixxie]

It would also be really great if this was visible in the README; currently, the tag in the README shows the latest version of DuckDB regardless of the one used:

  <a href="https://github.com/duckdb/duckdb/releases/">
    <img src="https://img.shields.io/github/v/release/duckdb/duckdb?color=brightgreen&display_name=tag&logo=duckdb&logoColor=white" alt="Latest DuckDB Release">
  </a>

[ixxie]

Additionally, you could also consider exporting a variable called DATABASE_VERSION similar to PACKAGE_VERSION available for DuckDB WASM itself. Identical version parts for _MAJOR, _MINOR and _PATCH would be handy too.