Add missing API docs about filtering by label.

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

docs/sources/reference/api/docker_remote_api_v1.18.md

@@ -91,6 +91,7 @@ Query Parameters:
 -   **filters** - a json encoded value of the filters (a map[string][]string) to process on the containers list. Available filters:
   -   exited=<int> -- containers with exit code of <int>
   -   status=(restarting|running|paused|exited)
+  -   label=`key` or `key=value` of a container label
 
 Status Codes:
 
@@ -1191,6 +1192,7 @@ Query Parameters:
 -   **all** – 1/True/true or 0/False/false, default false
 -   **filters** – a json encoded value of the filters (a map[string][]string) to process on the images list. Available filters:
   -   dangling=true
+  -   label=`key` or `key=value` of an image label
 
 ### Build image from a Dockerfile
 

docs/sources/reference/api/docker_remote_api_v1.19.md

@@ -91,6 +91,7 @@ Query Parameters:
 -   **filters** - a json encoded value of the filters (a map[string][]string) to process on the containers list. Available filters:
   -   exited=<int> -- containers with exit code of <int>
   -   status=(restarting|running|paused|exited)
+  -   label=`key` or `key=value` of a container label
 
 Status Codes:
 
@@ -1194,6 +1195,7 @@ Query Parameters:
 -   **all** – 1/True/true or 0/False/false, default false
 -   **filters** – a json encoded value of the filters (a map[string][]string) to process on the images list. Available filters:
   -   dangling=true
+  -   label=`key` or `key=value` of an image label
 
 ### Build image from a Dockerfile