Update cable length between LT2, FT2 and UT2 (#23686)

Update cable length between LT2, FT2 and UT2

Author: bingwang-ms

files/build_templates/buffers_config.j2

@@ -62,6 +62,8 @@ def
             'upperspinerouter_spinerouter' : '30m',
             'upperspinerouter_lowerspinerouter' : '30m',
             'spinerouter_leafrouter' : '300m',
+            'lowerspinerouter_leafrouter' : '500m',
+            'fabricspinerouter_lowerspinerouter' : '5m',
             'regionalhub_upperspinerouter': '80000m',
             'regionalhub_spinerouter': '80000m',
             'aznghub_upperspinerouter'    : '80000m',