Adds a new parameter to the BlobContainer#write*Blob methods to specify whether the existing file
should be overridden or not. For some metadata files in the repository, we actually want to replace
the current file. This is currently implemented through an explicit blob delete and then a fresh write.
In case of using a cloud provider (S3, GCS, Azure), this results in 2 API requests instead of just 1.
This change will therefore allow us to achieve the same functionality using less API requests.
2bb4f38371