feat(ESPAT-2194): Added a fatfs_to_http_server example

examples/at_fatfs_to_http_server/CMakeLists.txt

@@ -0,0 +1,14 @@
+
+file(GLOB_RECURSE srcs *.c)
+
+set(includes "include")
+
+# Add more required components you need here, separated by spaces
+set(require_components at freertos esp_http_client)
+
+idf_component_register(
+    SRCS ${srcs}
+    INCLUDE_DIRS ${includes}
+    REQUIRES ${require_components})
+
+idf_component_set_property(${COMPONENT_NAME} WHOLE_ARCHIVE TRUE)

examples/at_fatfs_to_http_server/README.md

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+### Usage
+1. Add this `at_fatfs_to_http_server` component into the build system of esp-at project.
+
+- Linux or macOS
+```
+export AT_CUSTOM_COMPONENTS=(path_of_at_custom_cmd)
+```
+
+- Windows
+```
+set AT_CUSTOM_COMPONENTS=(path_of_at_custom_cmd)
+```
+
+Notes:
+- You need to replace (path_of_at_custom_cmd) with your real absolute path of your `at_custom_cmd` directory.
+- You can specify multiple components. For example: `export AT_CUSTOM_COMPONENTS="~/prefix/my_path1 ~/prefix/my_path2"`.
+
+2. Compile your firmware according to the [Compile ESP-AT Project](https://docs.espressif.com/projects/esp-at/en/latest/esp32/Compile_and_Develop/How_to_clone_project_and_compile_it.html#compile-esp-at-project-locally) guide.
+
+3. Send a new AT command based on your situation.
+
+The new command format is:
+```
+AT+FS_TO_HTTP_SERVER=<"dst_path">,<url_len>
+```
+where:
+- <"dst_path">: Specify the destination path where the file will be posted from the filesystem after the HTTP POST request is successfully executed.
+- <url_len>: URL length. Maximum: 8192 bytes.
+
+For example: url is "http://httpbin.org/post", and you want to post file `foo.bin`.
+```
+AT+FS_TO_HTTP_SERVER="foo.bin",23
+// then input http://httpbin.org/post
+```