Update 02.docker.md (#2495)

Better like this:
- the end quote was missing
- this preserves the new lines when copy pasted 🎉

Author: fdelbrayelle

content/docs/02.installation/02.docker.md

@@ -81,30 +81,31 @@ Managing a large configuration via a single YAML string can be tedious. To make
 First, define an environment variable:
 
 ```bash
-export KESTRA_CONFIGURATION="datasources:
-          postgres:
-            url: jdbc:postgresql://postgres:5432/kestra
-            driverClassName: org.postgresql.Driver
-            username: kestra
-            password: k3str4
-        kestra:
-          server:
-            basicAuth:
-              enabled: false
-              username: "[email protected]" # it must be a valid email address
-              password: kestra
-          repository:
-            type: postgres
-          storage:
-            type: local
-            local:
-              basePath: "/app/storage"
-          queue:
-            type: postgres
-          tasks:
-            tmpDir:
-              path: /tmp/kestra-wd/tmp
-          url: http://localhost:8080/
+export KESTRA_CONFIGURATION=$'
+datasources:
+  postgres:
+    url: jdbc:postgresql://postgres:5432/kestra
+    driverClassName: org.postgresql.Driver
+    username: kestra
+    password: k3str4
+kestra:
+  server:
+    basicAuth:
+      enabled: false
+      username: "[email protected]" # it must be a valid email address
+      password: kestra
+  repository:
+    type: postgres
+  storage:
+    type: local
+    local:
+      basePath: "/app/storage"
+  queue:
+    type: postgres
+  tasks:
+    tmpDir:
+      path: /tmp/kestra-wd/tmp
+  url: http://localhost:8080/'
 ```
 
 ::alert{type="info"}