Add a minimal test database setup to the docker-compose file (#16305)

This provides a test environment database for anyone using a docker
based development environment.

Expose, rather than bind, the db port (you won't be able to connect to
the db externally, only from the container).

Add tmpfs storage (this alleviates an issue seen with carrierwave
attachments when trying to write to the tmp directory in the image).

Upgrade db versions from 11 to 13 (this is a breaking change for
anyone using this who had already provisioned the db, since no attempt
to upgrade has been provided, users may either downgrade to the
11-alpine image or recreate their storage volume). This is
separable (the `db` container was preexisting so is the only upgrade
conflict for users, the `testdb` container is newly created in a newly
added volume, and should not rely on persistence).

It's possible no volume is needed for the test db (only the schema
would normally be persisted, since data is truncated after normal test completion).

docker-compose.yml

@@ -11,9 +11,11 @@ services:
       - db
       - redis
       - yarn
+      - testdb
     environment:
       RAILS_ENV: development
       DATABASE_URL: postgresql://forem:forem@db:5432/PracticalDeveloper_development
+      DATABASE_URL_TEST: postgresql://forem:forem@testdb:5432/Forem_test
       REDIS_SESSIONS_URL: redis://redis:6379
       REDIS_SIDEKIQ_URL: redis://redis:6379
       REDIS_URL: redis://redis:6379
@@ -21,6 +23,8 @@ services:
       RACK_TIMEOUT_SERVICE_TIMEOUT: 10000
       STATEMENT_TIMEOUT: 10000
       APP_DOMAIN: localhost:3000
+    tmpfs:
+      - /tmp
     volumes:
       - .:/opt/apps/forem:delegated
     entrypoint: ["dockerize", "-wait", "tcp://db:5432", "-wait", "tcp://redis:6379", "-wait", "file:///opt/apps/forem/vendor/bundle/.bundle_finished", "-timeout", "2700s", "-wait-retry-interval", "10s"]
@@ -112,7 +116,7 @@ services:
     command: ["bundle", "exec", "sidekiq","-c","2"]
 
   db:
-    image: postgres:11-alpine
+    image: postgres:13-alpine
     container_name: forem_postgresql
     environment:
       POSTGRES_USER: forem
@@ -123,6 +127,18 @@ services:
     volumes:
       - db_data:/var/lib/postgresql/data:delegated
 
+  testdb:
+    image: postgres:13-alpine
+    container_name: forem_postgresql_test
+    environment:
+      POSTGRES_USER: forem
+      POSTGRES_PASSWORD: forem
+      POSTGRES_DB: Forem_test
+    expose:
+      - "5432"
+    volumes:
+      - testdb_data:/var/lib/postgresql/data:delegated
+
   redis:
     image: redis:6.0.9-alpine
     container_name: forem_redis
@@ -131,3 +147,4 @@ services:
 
 volumes:
   db_data:
+  testdb_data: