Bump version to 5.5.0 #339

Job	Run time
check / clang-checks	1m 10s
check / editor-config	11s
build-os-matrix	3s
build (oraclelinux:10) / build	1m 56s
make-tests (oraclelinux:10) / tests	1m 29s
rpm-build (oraclelinux:10) / rpm-build	5m 45s
ipfix-elements-check / ipfix-elements-checks	17s
rpm-install (oraclelinux:10) / rpm-install	57s
	11m 48s

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