feat(xiao_s3): add kiss modem env

variants/xiao_s3/platformio.ini

@@ -151,4 +151,9 @@ build_flags =
 ;  -D MESH_DEBUG=1
 lib_deps =
   ${Xiao_S3.lib_deps}
-  ${esp32_ota.lib_deps}
+  ${esp32_ota.lib_deps}
+
+[env:Xiao_S3_kiss_modem]
+extends = Xiao_S3
+build_src_filter = ${Xiao_S3.build_src_filter}
+  +<../examples/kiss_modem/>