Default folder permissions on linux systems for generated instances

[bobbah]

Describe the bug Instances generated by TGS on Debian 10 appear to have rather permissive 755 permissions.

To Reproduce Steps to reproduce the behavior:

1. Create instance on a linux TGS4 server
2. Review permissions on created directories

Expected behavior I think it would be reasonable to have the generated directories and contents be 700, or 750, to prevent all users on the filesystem being able to read potentially sensitive logs and configuration values.

Logs n/a

Server State: (please complete the following information):

• OS: Debian 10
• Version: TGS 4.10.5 docker image
• Database Type/Version: Postgres 13.1
• BYOND Version Used: n/a
• git Repository Used: n/a
• Origin Commit hash Used: n/a
• Active Test Merges: n/a
• Client Version: TGS desktop client 2.1.1

[Cyberboss]

I think this is something to do with dotnet because we just use Directory.CreateDirectory here https://github.com/tgstation/tgstation-server/blob/5b6c0c90fe6dba74b28a518e722544923039baec/src/Tgstation.Server.Host/IO/DefaultIOManager.cs#L159