Add function 'setPoolServerIP' like 'setPoolServerName'

[vmsh0]

As the title suggests, adds 'setPoolServerIP' that allows to change the server pool IP address after instantiation akin to how it's possible to change the server DNS name

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Resolves https://github.com/arduino-libraries/NTPClient/issues/103

[CLAassistant]

All committers have signed the CLA.

[github-actions[bot]]

Memory usage change @ 394e8839bc4888a6671398a90294e75a3c1f6ac9

Board	flash	%	RAM for global variables	%
esp8266:esp8266:huzzah	N/A	N/A	N/A	N/A

Click for full report table

Board	examples/Advanced flash	%	examples/Advanced RAM for global variables	%	examples/Basic flash	%	examples/Basic RAM for global variables	%	examples/IsTimeSet flash	%	examples/IsTimeSet RAM for global variables	%
esp8266:esp8266:huzzah	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A

Click for full report CSV

Board,examples/Advanced<br>flash,%,examples/Advanced<br>RAM for global variables,%,examples/Basic<br>flash,%,examples/Basic<br>RAM for global variables,%,examples/IsTimeSet<br>flash,%,examples/IsTimeSet<br>RAM for global variables,%
esp8266:esp8266:huzzah,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A