[exporter/prometheusremotewrite] change feature gate to beta (#36606) #17355

Job	Run time
arm-unittest-matrix (receiver-0)	5m 12s
arm-unittest-matrix (receiver-1)	6m 43s
arm-unittest-matrix (receiver-2)	8m 3s
arm-unittest-matrix (receiver-3)	6m 35s
arm-unittest-matrix (processor-0)	3m 34s
arm-unittest-matrix (processor-1)	4m 29s
arm-unittest-matrix (exporter-0)	3m 19s
arm-unittest-matrix (exporter-1)	10m 4s
arm-unittest-matrix (exporter-2)	4m 12s
arm-unittest-matrix (exporter-3)	5m 4s
arm-unittest-matrix (extension)	4m 59s
arm-unittest-matrix (connector)	5m 58s
arm-unittest-matrix (internal)	6m 19s
arm-unittest-matrix (pkg)	4m 1s
arm-unittest-matrix (cmd-0)	3m 24s
arm-unittest-matrix (cmd-1)	4m 19s
arm-unittest-matrix (other)	4m 42s
arm-unittest	0s
	1h 30m 57s

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