Remove cmake from the build process

While I'm here change the name of the module to ngx_otel_module.

config.make

@@ -1,10 +1,45 @@
-cat << END >> $NGX_MAKEFILE
+if [ ! "`which protoc 2>/dev/null`" ]; then
+    echo "Need to install protoc."
+    exit 2
+else
+    PROTOC=`which protoc`
+fi
 
-modules: ngx_otel_module
+if [ ! "`which grpc_cpp_plugin 2>/dev/null`" ]; then
+    echo "Need to install grpc tools."
+    exit 2
+else
+    GRPC_CPP=`which grpc_cpp_plugin`
+fi
 
-ngx_otel_module:
-	\$(MAKE) -C $NGX_OBJS/otel
+mkdir -p objs
 
-.PHONY: ngx_otel_module
+if [ -z $NGX_OTEL_PROTO_DIR ]; then
+    echo "Need to set \$NGX_OTEL_PROTO_DIR variable."
+    exit 2
+fi
 
-END
+if [ ! -d $NGX_OTEL_PROTO_DIR ]; then
+    echo "\$NGX_OTEL_PROTO_DIR is set to unavailable directory."
+    exit 2
+fi
+
+find $NGX_OTEL_PROTO_DIR/opentelemetry/proto -type f -name '*.proto' | \
+    xargs $PROTOC \
+        --proto_path $NGX_OTEL_PROTO_DIR \
+        --cpp_out=objs \
+        --grpc_out=objs \
+        --plugin=protoc-gen-grpc=$GRPC_CPP
+
+find objs -name '*.pb.cc' | \
+    xargs sed -i.bak -e "/    ::PROTOBUF_NAMESPACE_ID::internal::WireFormatLite::VerifyUtf8String(/,/);/d"
+
+for src_file in $OTEL_NGX_SRCS; do
+    obj_file="$NGX_OBJS/addon/src/`basename $src_file .cpp`.o"
+    echo "$obj_file : CFLAGS += $CXXFLAGS -Wno-missing-field-initializers -Wno-conditional-uninitialized -fPIC -fvisibility=hidden -DHAVE_ABSEIL -Dngx_otel_module_EXPORTS" >> $NGX_MAKEFILE
+done
+
+for src_file in $OTEL_NGX_SRCS; do
+    obj_file="$NGX_OBJS/addon/v1/`basename $src_file .cc`.o"
+    echo "$obj_file : CFLAGS += $CXXFLAGS -Wno-missing-field-initializers -Wno-conditional-uninitialized -fPIC -fvisibility=hidden -DHAVE_ABSEIL -Dngx_otel_module_EXPORTS" >> $NGX_MAKEFILE
+done