Add the possibility to restart OTA multiple times

[pennam]

Add the possibility to restart OTA multiple times on error or success keeping the same global object:

• Initialize variables inside begin()
• Ensure _client is always deleted returning from download function

[pennam]

rebased on master to resolve conflicts

[github-actions]

Memory usage change @ c644a2f

Board	flash	%	RAM for global variables	%
arduino:esp32:nano_nora	🔺 0 - +220	0.0 - +0.01	0 - 0	0.0 - 0.0
esp32:esp32:esp32	🔺 0 - +224	0.0 - +0.02	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/OTA_Arduino_Server flash	%	examples/OTA_Arduino_Server RAM for global variables	%	examples/OTA_GitHub_Server flash	%	examples/OTA_GitHub_Server RAM for global variables	%	examples/NANO_ESP32_Blink flash	%	examples/NANO_ESP32_Blink RAM for global variables	%	examples/LOLIN_32_Blink flash	%	examples/LOLIN_32_Blink RAM for global variables	%
arduino:esp32:nano_nora	220	0.01	0	0.0	220	0.01	0	0.0	0	0.0	0	0.0
esp32:esp32:esp32	224	0.02	0	0.0	224	0.02	0	0.0					0	0.0	0	0.0

Click for full report CSV

Board,examples/OTA_Arduino_Server<br>flash,%,examples/OTA_Arduino_Server<br>RAM for global variables,%,examples/OTA_GitHub_Server<br>flash,%,examples/OTA_GitHub_Server<br>RAM for global variables,%,examples/NANO_ESP32_Blink<br>flash,%,examples/NANO_ESP32_Blink<br>RAM for global variables,%,examples/LOLIN_32_Blink<br>flash,%,examples/LOLIN_32_Blink<br>RAM for global variables,%
arduino:esp32:nano_nora,220,0.01,0,0.0,220,0.01,0,0.0,0,0.0,0,0.0
esp32:esp32:esp32,224,0.02,0,0.0,224,0.02,0,0.0,,,,,0,0.0,0,0.0