[Library Manager] Please add AsyncWebServer_STM32 Library

[khoih-prog]

Please add AsyncWebServer_STM32 to Library Manager.
Thanks and Regards.

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Initial Releases v1.2.3

1. Initial coding to port ESPAsyncWebServer to STM32 boards using builtin LAN8742A Ethernet. More supports will be added gradually later, such as AsyncUDP, other Ethernet / WiFi shields.
2. Add more examples.
3. Add debugging features.
4. Bump up to v1.2.3 to sync with ESPAsyncWebServer v1.2.3.

Currently Supported Boards

1. Nucleo-144 (F429ZI, F746ZG, F756ZG, F767ZI)
2. Discovery STM32F746G-DISCOVERY
3. Any STM32 boards with enough flash/memory and already configured to run LAN8742A Ethernet.

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Async HTTP and WebSocket Server for STM32 boards using builtin LAN8742A Ethernet

This library is based on, modified from:

1. Hristo Gochkov's ESPAsyncWebServer

to apply the better and faster asynchronous feature of the powerful ESPAsyncWebServer Library into STM32 boards using builtin LAN8742A Ethernet.

[cmaglie]

Done.