docker: allow to configure Invidious by env var

Invidious gained support to read its configuration from an env var
instead of config file in e3c10d779d315adc630e08005b6bdbdce32f7446.

Unfortunately, Docker doesn't allow newline characters in env var
values (see [0]) which means we can only provide a proper YAML config
by using the inlined configuration in docker-compose.yml which,
unfortunately, is tracked by Git. Once support for multiline env var
values has been added to Docker, we should migrate and read the config
from a .env file instead (which is not tracked by Git).

[0]: https://github.com/docker/compose/issues/3527

docker-compose.yml

@@ -16,6 +16,20 @@ services:
     restart: unless-stopped
     ports:
       - "127.0.0.1:3000:3000"
+    environment:
+      # Adapted from ./config/config.yml
+      INVIDIOUS_CONFIG: |
+        channel_threads: 1
+        feed_threads: 1
+        db:
+          user: kemal
+          password: kemal
+          host: postgres
+          port: 5432
+          dbname: invidious
+        full_refresh: false
+        https_only: false
+        domain:
     depends_on:
       - postgres