Clarify filters option in list containers and list images docs

Based on the list containers with filters options it would seem that filtering containers with label `test=docker-java` could be done with `{"test":["docker-java"]}` which doesn't work

The options that work are `{"label":["test"]}` and `{"label":["test=docker-java"]}`

As seen in https://github.com/docker-java/docker-java/pull/262

Signed-off-by: Carlos Sanchez <carlos@apache.org>

docs/reference/api/docker_remote_api_v1.18.md

@@ -102,7 +102,7 @@ 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
+  -   label=`key` or `label="key=value"` of a container label
 
 Status Codes:
 
@@ -1126,7 +1126,7 @@ 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
+  -   label=`key` or `label="key=value"` of an image label
 -   **filter** - only return images with the specified name
 
 ### Build image from a Dockerfile

docs/reference/api/docker_remote_api_v1.19.md

@@ -104,7 +104,7 @@ 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
+  -   `label=key` or `label="key=value"` of a container label
 
 Status Codes:
 
@@ -1145,7 +1145,7 @@ 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
+  -   `label=key` or `label="key=value"` of an image label
 -   **filter** - only return images with the specified name
 
 ### Build image from a Dockerfile

docs/reference/api/docker_remote_api_v1.20.md

@@ -104,7 +104,7 @@ 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=`(`created`|`restarting`|`running`|`paused`|`exited`)
-  -   `label=key` or `key=value` of a container label
+  -   `label=key` or `label="key=value"` of a container label
 
 Status Codes:
 
@@ -1272,7 +1272,7 @@ 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
+  -   `label=key` or `label="key=value"` of an image label
 -   **filter** - only return images with the specified name
 
 ### Build image from a Dockerfile