Create restic users and generate S3 credentials

We create the accounts per container and server:

• for -amaris, every server
• for -darak, WindRiver as experimental test
• for -vakor, Complector

These 13 accounts are separate OVH project users,
with separate credentials stored in Vault.

-amaris accounts are intended to be included in by-server Vault policy,
-vakor account can use an approle, as an unprivileged account can do this.

Differential Revision: https://devcentral.nasqueron.org/D4206