Add storage independent state versioning

[lu1as]

Terraform state files should be versioned to have a backup in case of Terraform issues or users pushing an incorrect state by accident. Currently we rely on the versioning features of the underlying storage, if available (e.g. S3 bucket versioning).

It would be nice to integrate an API endpoint for fetching older state versions and add an independent versioning which works for all storage backends, even if the storage itself doens't support it.