Add docker files

docker/backend.entrypoint.sh

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+
+fail() {
+    printf '%s\n' "$1" >&2 ## Send message to stderr.
+    exit "${2-1}"          ## Return a code specified by $2, or 1 by default.
+}
+
+[[ -d migrations ]] || fail "Error: Must be run from the backend directory."
+[[ -d /opt/sshecret-backend-db ]] || mkdir /opt/sshecret-backend-db
+
+export SSHECRET_BACKEND_DATABASE="/opt/sshecret-backend-db/sshecret.db"
+
+alembic upgrade head
+
+sshecret-backend run --host 0.0.0.0