Show a color ramp legend for vector heatmap layers #30206

Job	Run time
build (22.04, 5, true, OFF, ON, ON, ON, ON, OFF, OFF, OFF, OFF, ON, false)	1h 0m 26s
build (39, 6, true, ON, OFF, ON, ON, OFF, OFF, ON, ON, ON, OFF, false)	1h 49m 41s
clang-tidy (22.04, 5)	7m 7s
Run tests (5, ALL_BUT_PROVIDERS)	31m 49s
Run tests (5, POSTGRES)	7m 3s
Run tests (5, HANA)	12m 28s
Run tests (6, ALL_BUT_PROVIDERS)	31m 1s
Run tests (5, ORACLE, 22.04, binary-for-oracle)	7m 3s
	4h 26m 38s

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