[exporter/prometheusremotewrite] change feature gate to beta (#36606) #95761

Job	Run time
windows-unittest-matrix (receiver-0)	14m 46s
windows-unittest-matrix (receiver-1)	16m 5s
windows-unittest-matrix (receiver-2)	15m 3s
windows-unittest-matrix (receiver-3)	15m 28s
windows-unittest-matrix (processor-0)	8m 55s
windows-unittest-matrix (processor-1)	10m 15s
windows-unittest-matrix (exporter-0)	9m 54s
windows-unittest-matrix (exporter-1)	21m 26s
windows-unittest-matrix (exporter-2)	9m 50s
windows-unittest-matrix (exporter-3)	9m 54s
windows-unittest-matrix (extension)	20m 59s
windows-unittest-matrix (connector)	9m 12s
windows-unittest-matrix (internal)	13m 56s
windows-unittest-matrix (pkg)	9m 38s
windows-unittest-matrix (cmd-0)	4m 31s
windows-unittest-matrix (cmd-1)	3m 59s
windows-unittest-matrix (other)	10m 33s
windows-unittest	0s
	3h 24m 24s

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