home-assistant: Manage YAML files with ConfigMap

Editing `configuration.yaml` et al. using `vi` via `kubectl exec` is
rather tedious, since the version of `vi` in the *home-assistant*
container image is very rudimentary.  Thus, I think it would be better
to use a ConfigMap to store the manually-edited YAML files, so I can
edit them with my regular editor on my desktop.  For this to work, the
ConfigMap has to be mounted as a directory rather than as individual
files (using `subPath`), as otherwise the pod would have to be restarted
every time one of the files is updated.

home-assistant/groups.yaml

@@ -0,0 +1,15 @@
+family:
+  entities:
+  - person.dustin
+  - person.tabitha
+  name: Family
+watch_view:
+  entities:
+  - cover.garage_door_3
+  - cover.garage_door_2
+  - cover.garage_door_1
+  - light.front_porch_light
+  - light.back_porch_light
+  - light.back_porch_flood_light
+  - light.garage_lights
+  name: Watch View