snackpot.yml etc. - refine docker-compose config deploy

The main job of this commit:
- Be explicit about templates: expect the .j2 extension
- Copy all other files, so that they can be binary
- Don't deploy dotfiles or dotdirectories.

This snuck in:
- Remove `test` tag
- Refine some descriptions

templates/docker-compose/postgres/Dockerfile.j2

@@ -0,0 +1,2 @@
+FROM postgres:11.9-alpine
+COPY --chown={{ postgres_db_user }}:{{ postgres_db_user }} init.sql /docker-entrypoint-initdb.d/