Store images in DB

**Is your feature request related to a problem? Please describe.**
I have a multi-node cluster and whenever the node Gotify is scheduled onto changes, I need to copy data folder to preserve favicons. I'm using postgresql to preserve configuration wherever Gotify is scheduled on the cluster. However this doesn't apply to images and I think this is a quality of life gap.

**Describe the solution you'd like**
I would like Gotify to store blobs in database and not directly on disk.

**Describe alternatives you've considered**
I considered either scheduling Gotify on a fixed node or having a multinode disk to sync configuration. However as a user, I would like to keep things simple and not have to think about scheduling or GlusterFS like solutions.

**Additional context**
https://github.com/arch-anes/self-hosted-services/blob/94b6630b05586b8bb24ee3444b00755994d0ba7b/kubernetes/services/gotify.yml