(cherry picked from commit ce760c6)

# Conflicts:
#	.github/workflows/test-management-ui-for-pr.yaml
#	deps/rabbitmq_management/test/rabbit_mgmt_http_SUITE.erl
#	selenium/test/multi-oauth/certs/server_rabbitmq_certificate.pem
#	selenium/test/multi-oauth/certs/server_rabbitmq_key.pem
#	selenium/test/multi-oauth/devkeycloak/server_devkeycloak.p12
#	selenium/test/multi-oauth/devkeycloak/server_devkeycloak_certificate.pem
#	selenium/test/multi-oauth/devkeycloak/server_devkeycloak_key.pem
#	selenium/test/multi-oauth/prodkeycloak/server_prodkeycloak.p12
#	selenium/test/multi-oauth/prodkeycloak/server_prodkeycloak_certificate.pem
#	selenium/test/multi-oauth/prodkeycloak/server_prodkeycloak_key.pem

(cherry picked from commit 50a316a)

rabbit:product_version/0 should not return
an 'undefined'.

However, a fallback to the base version is
a technique we already use in 'rabbitmq-diagnostics status',
so adopt the same trick.

(cherry picked from commit f5a8388)