Population as of end of 2021.

[bgrundmann]

Taken from destatis (minus some areas we are not interested in). See https://github.com/GermanZero-de/localzero-generator-core/blob/0378c4b9280c4a4fc6c2e029aa3e6082f334c5c5/exploration-and-data-generation/tooling-data-prepration/tool.py#L20