Implement configurable detach key

Implement configurable detach keys (for `attach`, exec`, `run` and
`start`) using the client-side configuration

- Adds a `--detach-keys` flag to `attach`, `exec`, `run` and `start`
  commands.
- Adds a new configuration field (in `~/.docker/config.json`) to
  configure the default escape keys for docker client.

Signed-off-by: Vincent Demeester <vincent@sbr.pm>
Upstream-commit: 15aa2a663b47b6126a66efefcadb64edfbffb9f5
Component: engine

components/engine/docs/reference/commandline/cli.md

@@ -101,7 +101,26 @@ The property `psFormat` specifies the default format for `docker ps` output.
 When the `--format` flag is not provided with the `docker ps` command,
 Docker's client uses this property. If this property is not set, the client
 falls back to the default table format. For a list of supported formatting
-directives, see the [**Formatting** section in the `docker ps` documentation](ps.md)
+directives, see the
+[**Formatting** section in the `docker ps` documentation](ps.md)
+
+Once attached to a container, users detach from it and leave it running using
+the using `CTRL-p CTRL-q` key sequence. This detach key sequence is customizable
+using the `detachKeys` property. Specify a `<sequence>` value for the
+property. The format of the `<sequence>` is either a letter [a-Z], or the `ctrl-`
+combined with any of the following:
+
+* `a-z` (a single lowercase alpha character )
+* `@` (ampersand)
+* `[` (left bracket)
+* `\\` (two backward slashes)
+*  `_` (underscore)
+* `^` (caret)
+
+Your customization applies to all containers started in with your Docker client.
+Users can override your custom or the default key sequence on a per-container
+basis. To do this, the user specifies the `--detach-keys` flag with the `docker
+attach`, `docker exec`, `docker run` or `docker start` command.
 
 The property `imagesFormat` specifies the default format for `docker images` output.
 When the `--format` flag is not provided with the `docker images` command,
@@ -115,8 +134,9 @@ Following is a sample `config.json` file:
       "HttpHeaders": {
         "MyHeader": "MyValue"
       },
-      "psFormat": "table {{.ID}}\\t{{.Image}}\\t{{.Command}}\\t{{.Labels}}"
-      "imagesFormat": "table {{.ID}}\\t{{.Repository}}\\t{{.Tag}}\\t{{.CreatedAt}}"
+      "psFormat": "table {{.ID}}\\t{{.Image}}\\t{{.Command}}\\t{{.Labels}}",
+      "imagesFormat": "table {{.ID}}\\t{{.Repository}}\\t{{.Tag}}\\t{{.CreatedAt}}",
+      "detachKeys": "ctrl-e,e"
     }
 
 ### Notary