Document proper ransomware protection setups

[deajan]

Since we're using various ransomware protection, let's document it:

• rest server --append mode and housekeeping server
• S3 server IAM delete restrictions (which is strictly saying not sufficient since we still could overwrite existing files) without versionning and housekeeping server
• S3 ILM mode and housekeeping client

[deajan]

Since minio has changed their licence, we must check with garageS3 and rustfs (the latter being a good drop-in replacement, but not yet production grade).