Add cache list command

This introduces a new cache sub-command that lists all available
caches.

Relates-to: python-poetry#1162

docs/docs/cli.md

@@ -513,3 +513,15 @@ poetry env remove test-O3eWbxRl-py3.7
 !!!note
 
     If your remove the currently activated virtualenv, it will be automatically deactivated.
+
+## cache
+
+The `cache` command regroups sub commands to interact with Poetry's cache.
+
+### cache list
+
+The `cache list` command lists Poetry's available caches.
+
+```bash
+poetry cache list
+```

poetry/console/commands/cache/cache.py

@@ -1,3 +1,4 @@
+from poetry.console.commands.cache.list import CacheListCommand
 from ..command import Command
 
 from .clear import CacheClearCommand
@@ -8,7 +9,7 @@ class CacheCommand(Command):
     name = "cache"
     description = "Interact with Poetry's cache"
 
-    commands = [CacheClearCommand()]
+    commands = [CacheClearCommand(), CacheListCommand()]
 
     def handle(self):
         return self.call("help", self._config.name)