Allow to add additional binds to Docker build container (#7684)

* Allow to add additional binds to Docker build container

Sometimes it might be necessary to add additional binds to the build
container, e.g. to add SSH keys for the docs user to clone private
repositories or for caches. These additional binds can be specified
as field in settings:

RTD_DOCKER_ADDITIONAL_BINDS = {
  '/home/docs/.ssh': {
    'bind': '/home/docs/.ssh',
    'mode': 'ro',
  }
}

Author: fabianmp

readthedocs/doc_builder/environments.py

@@ -991,6 +991,8 @@ def _get_binds(self):
                 },
             }
 
+        binds.update(settings.RTD_DOCKER_ADDITIONAL_BINDS)
+
         return binds
 
     def get_container_host_config(self):

readthedocs/settings/base.py

@@ -497,6 +497,8 @@ def TEMPLATES(self):
         'readthedocs/build:latest': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:6.0'),
         'readthedocs/build:testing': DOCKER_IMAGE_SETTINGS.get('readthedocs/build:7.0'),
     })
+    # Additional binds for the build container
+    RTD_DOCKER_ADDITIONAL_BINDS = {}
 
     def _get_docker_memory_limit(self):
         try: