feat: Set up filesystems

Automatically set up btrfs root and data filesystem, as well as external
HDD.

This automation change assumes a layout exactly as in current bob to
function by default, can be changed to any btrfs layout with the
`btrfs_mounts` configuration option, however.

roles/filesystem/README.md

@@ -0,0 +1,38 @@
+filesystem
+=========
+
+Mounts the filesystem(s) required for bob.
+Focused on correct `btrfs` layout and mounting,
+but also mounts an external `ext4` HDD by default.
+
+Requirements
+------------
+
+This role requires a btrfs filesystem _existing_ on _any device_ that is targeted with the role (using the 'btrfs_mounts') configuration option.
+Optionally, an external HDD is required if the mount toggle is true.
+
+Role Variables
+--------------
+
+`btrfs_mounts` can be used to set up the various (top-level) btrfs subvolumes, and their later mount points in the system.
+Define an entry by giving the `uuid` of the targeted btrfs filesystem (or device), give the name of the `subvol` you intend to give, and define the `path` where it should ultimately be mounted by `fstab`.
+You can additionally provide some `opts` which are given to `fstab` for the mount process as well.
+
+Example:
+
+```yaml
+btrfs_mounts:
+  - path: "/home"
+    subvol: "@home"
+    uuid: "3204f33f-5fa7-4c11-bdd8-979c539fce91"
+    opts: "defaults,ssd,noatime,compress=zstd:3,space_cache=v2"
+
+  - path: "/srv/media"
+    subvol: "@media"
+    uuid: "2256bd23-7751-486a-bfc4-b216a6b0c4f4"
+    opts: "defaults,noatime,compress=zstd:3,space_cache=v2"
+```
+
+---
+
+`should_mount_external_hdd` can be toggled to automatically mount a USB-connected HDD on boot, or not.