docker: Libervia revision can now be specified:

Using the `DOCKER_LIBERVIA_REV` environment variable, backend (and related repos) revision
can now be specified. By default (variable empty or not set), the current `tip` version is
used, and `dev` is used for tagging. If the variable is set, the revision will be used and
used for tagging the image.

docker/docker-compose.yml

@@ -2,11 +2,17 @@ version: "3.6"
 services:
 
   backend:
-    image: libervia/backend:dev
-    build: backend-dev
+    image: "libervia/backend:${DOCKER_LIBERVIA_REV:-dev}"
+    build:
+      context: backend-dev
+      args:
+        REVISION: "${DOCKER_LIBERVIA_REV:-}"
 
   web:
-    image: libervia/web:dev
-    build: libervia-web-dev
+    image: "libervia/web:${DOCKER_LIBERVIA_REV:-dev}"
+    build:
+      context: libervia-web-dev
+      args:
+        REVISION: "${DOCKER_LIBERVIA_REV:-}"
     depends_on:
       - backend