Add AsyncMQTT_Generic Library

[khoih-prog]

Initial Releases v1.0.0

1. Initial porting and coding to support ESP32 (SSL and non-SSL) and ESP8266 (non-SSL)

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/khoih-prog/AsyncMQTT_Generic:

Linting library in AsyncMQTT_Generic
INFO: No header file found matching library name (AsyncMQTT_Generic.h). Best practices are for primary header filename  
      to match library name. (Rule LS008)                                                                               
WARNING: library.properties name value AsyncMQTT_Generic is longer than the recommended length of 16 characters. (Rule  
         LP010)                                                                                                         
WARNING: library.properties depends field item(s) ESPAsyncTCP, AsyncTCP, STM32AsyncTCP not found in the Library Manager 
         index. (Rule LP048)                                                                                            
WARNING: library.properties includes field item(s) AsyncMQTT_Generic.h not found in library. (Rule LP052)

Linter results for project: 0 ERRORS, 3 WARNINGS

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Linting sketch in AsyncMQTT_Generic/examples/ESP32/FullyFeaturedSSL_ESP32

Linter results for project: no errors or warnings

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Linting sketch in AsyncMQTT_Generic/examples/ESP32/FullyFeatured_ESP32

Linter results for project: no errors or warnings

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Linting sketch in AsyncMQTT_Generic/examples/ESP8266/FullyFeatured_ESP8266

Linter results for project: no errors or warnings

-------------------

Linter results for projects: 0 ERRORS, 3 WARNINGS

[github-actions]

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You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/khoih-prog/AsyncMQTT_Generic/