feat: upgrade to stellar protocol 27 #1595

Job	Run time
build	2m 56s
test reporter	2m 24s
test scaffold-cli (features)	6m 40s
test scaffold-cli (build_clients)	6m 51s
test scaffold-cli (examples 15-27)	7m 27s
test scaffold-cli (examples 1-14)	7m 59s
	34m 17s

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