Untrack config.yml (#1557)

* Untrack config.yml

`config/config.yml` has been untracked and moved to `config/config.example.yml`.

The Dockerfile has been updated to copy all `config/config.*` files and to try
to move `config/config.example.yml` to `config/config.yml`. If a user supplied
`config/config.yml` exists it is not overwritten.

* Update Dockerfile to use `shard.lock`

* Fix tests

config/config.example.yml

@@ -0,0 +1,11 @@
+channel_threads: 1
+feed_threads: 1
+db:
+  user: kemal
+  password: kemal
+  host: localhost
+  port: 5432
+  dbname: invidious
+full_refresh: false
+https_only: false
+domain: