[Docs] Merge GCP clusters examples (#3376)

Author: peterschmidt85

docs/docs/concepts/fleets.md

@@ -114,9 +114,7 @@ This ensures all instances are provisioned with optimal inter-node connectivity.
 
     !!! info "Backend configuration"    
         You may need to configure `extra_vpcs` and `roce_vpcs` in the `gcp` backend configuration.
-        Refer to the [A4](../../examples/clusters/a4/index.md),
-        [A3 Mega](../../examples/clusters/a3mega/index.md), and 
-        [A3 High](../../examples/clusters/a3high/index.md) examples for more details.
+        Refer to the [GCP](../../examples/clusters/gcp/index.md) examples for more details.
 
 ??? info "Nebius"
     When you create a fleet with Nebius, [InfiniBand networking](https://docs.nebius.com/compute/clusters/gpu) is automatically configured if it’s supported for the corresponding instance type.

docs/docs/guides/clusters.md

@@ -29,9 +29,7 @@ For cloud fleets, fast interconnect is currently supported only on the `aws`, `g
 
     !!! info "Backend configuration"    
         You may need to configure `extra_vpcs` and `roce_vpcs` in the `gcp` backend configuration.
-        Refer to the [A4](../../examples/clusters/a4/index.md),
-        [A3 Mega](../../examples/clusters/a3mega/index.md), and 
-        [A3 High](../../examples/clusters/a3high/index.md) examples for more details.
+        Refer to the [GCP](../../examples/clusters/gcp/index.md) examples for more details.
 
 === "Nebius"
     When you create a cloud fleet with Nebius, [InfiniBand](https://docs.nebius.com/compute/clusters/gpu) networking is automatically configured if it’s supported for the corresponding instance type.

docs/examples.md

@@ -100,37 +100,17 @@ hide:
             Run multi-node RCCL tests with MPI
         </p>
     </a>
-    <a href="/examples/clusters/a4"
+    <a href="/examples/clusters/gcp"
        class="feature-cell sky">
         <h3>
-            GCP A4
+            GCP
         </h3>
 
         <p>
-            Set up GCP A4 clusters with optimized networking
+            Set up GCP A4 and A3 clusters with optimized networking
         </p>
     </a>
-    <a href="/examples/clusters/a3mega"
-       class="feature-cell sky">
-        <h3>
-            GCP A3 Mega
-        </h3>
-
-        <p>
-            Set up GCP A3 Mega clusters with optimized networking
-        </p>
-    </a>
-    <a href="/examples/clusters/a3high"
-       class="feature-cell sky">
-        <h3>
-            GCP A3 High
-        </h3>
-
-        <p>
-            Set up GCP A3 High clusters with optimized networking
-        </p>
-    </a>
-        <a href="/examples/clusters/efa"
+    <a href="/examples/clusters/efa"
        class="feature-cell sky">
         <h3>
             AWS EFA