Add interface for Nginx build system.

config

@@ -0,0 +1,10 @@
+ngx_addon_name=ngx_otel_module
+
+cmake -D NGX_OTEL_NGINX_BUILD_DIR=$NGX_OBJS \
+      -D NGX_OTEL_FETCH_DEPS=OFF \
+      -D NGX_OTEL_PROTO_DIR=$NGX_OTEL_PROTO_DIR \
+      -D CMAKE_LIBRARY_OUTPUT_DIRECTORY=$PWD/$NGX_OBJS \
+      -D "CMAKE_C_FLAGS=$NGX_CC_OPT" \
+      -D "CMAKE_CXX_FLAGS=$NGX_CC_OPT" \
+      -D "CMAKE_MODULE_LINKER_FLAGS=$NGX_LD_OPT" \
+      -S $ngx_addon_dir -B $NGX_OBJS/otel || exit 1

config.make

@@ -0,0 +1,10 @@
+cat << END >> $NGX_MAKEFILE
+
+modules: ngx_otel_module
+
+ngx_otel_module:
+	make -C $NGX_OBJS/otel
+
+.PHONY: ngx_otel_module
+
+END