Updated docker-compose.yml: replaced broken images with latest

Fixed issues:
wso2/docs-apim#7405
https://github.com/wso2/samples-apim/issues/118

The docker-compose.yml contained references to 3 images with version '4.1.0'. However, those images don't exist (anymore?).

Therefore I updated these 3 references to point to version 'latest'. At this moment this will effectively result in version '4.0.0' being downloaded.

apim-tutorial/docker-compose.yml

@@ -1,7 +1,7 @@
 version: '2.4'
 services:
     api-manager:
-      image: wso2/wso2am:4.1.0
+      image: wso2/wso2am:latest
       healthcheck:
         test: ["CMD", "nc", "-z","localhost", "9443"]
         interval: 10s
@@ -24,7 +24,7 @@ services:
       build: 
         context: ./dockerfiles/micro-integrator/
         args:
-          - BASE_IMAGE=wso2/wso2mi:4.1.0
+          - BASE_IMAGE=wso2/wso2mi:latest
       healthcheck:
         test: ["CMD", "nc", "-z","localhost", "8290"]
         interval: 10s
@@ -51,7 +51,7 @@ services:
       build: 
         context: ./dockerfiles/streaming-integrator/
         args:
-          - BASE_IMAGE=wso2/wso2si:4.1.0
+          - BASE_IMAGE=wso2/wso2si:latest
       healthcheck:
         test: ["CMD", "nc", "-z","localhost", "9443"]
         interval: 10s