Use env varialbes to replace image urls & tags

Change-Id: I52421a03ddfb88fbad95eef8755c4d8e9c376705
Signed-off-by: ecaiyanlinux <martin.c.yan@est.tech>
Issue-ID: NONRTRIC-560
diff --git a/docker-compose/a1-sim/docker-compose.yaml b/docker-compose/a1-sim/docker-compose.yaml
index 9366ff1..8467946 100644
--- a/docker-compose/a1-sim/docker-compose.yaml
+++ b/docker-compose/a1-sim/docker-compose.yaml
@@ -22,7 +22,7 @@
 
 services:
   a1-sim-OSC:
-    image: nexus3.o-ran-sc.org:10002/o-ran-sc/a1-simulator:2.1.0
+    image: "${A1_SIM_IMAGE_BASE}:${A1_SIM_IMAGE_TAG}"
     container_name: a1-sim-OSC
     networks:
       - default
@@ -35,7 +35,7 @@
       - ALLOW_HTTP=true
 
   a1-sim-STD:
-    image: nexus3.o-ran-sc.org:10002/o-ran-sc/a1-simulator:2.1.0
+    image: "${A1_SIM_IMAGE_BASE}:${A1_SIM_IMAGE_TAG}"
     container_name: a1-sim-STD
     networks:
       - default
@@ -48,7 +48,7 @@
       - ALLOW_HTTP=true
 
   a1-sim-STD-v2:
-    image: nexus3.o-ran-sc.org:10002/o-ran-sc/a1-simulator:2.1.0
+    image: "${A1_SIM_IMAGE_BASE}:${A1_SIM_IMAGE_TAG}"
     container_name: a1-sim-STD-v2
     networks:
       - default