add kiss radio env to most of the variants

variants/heltec_v2/platformio.ini

@@ -195,3 +195,8 @@ build_src_filter = ${Heltec_lora32_v2.build_src_filter}
 lib_deps =
   ${Heltec_lora32_v2.lib_deps}
   densaugeo/base64 @ ~1.4.0
+
+[env:Heltec_v2_kiss_modem]
+extends = Heltec_lora32_v2
+build_src_filter = ${Heltec_lora32_v2.build_src_filter}
+  +<../examples/kiss_modem/>