Extend api with canardRxGetSubscription (#224) #255

Job	Run time
debug (clang)	23m 26s
optimizations (clang, Release)	12m 6s
debug (gcc)	27m 10s
avr	2m 40s
optimizations (clang, MinSizeRel)	12m 39s
arm	2m 31s
optimizations (gcc, Release)	10m 24s
optimizations (gcc, MinSizeRel)	9m 57s
sonarcloud	12m 12s
style_check	14s
	1h 53m 19s

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