add matcher cache for proxy store and tsdb store API #447

Job	Run time
Go build for different platforms	9m 46s
Go build with -tags=stringlabels	59s
Check misspelled words	10s
Thanos end-to-end tests (8, 0)	5m 18s
Linters (Static Analysis) for Go	2m 4s
Thanos end-to-end tests (8, 1)	3m 51s
Thanos end-to-end tests (8, 2)	4m 4s
Thanos unit tests	11m 5s
Thanos end-to-end tests (8, 3)	4m 30s
Thanos end-to-end tests (8, 4)	7m 14s
Thanos end-to-end tests (8, 5)	4m 17s
Thanos end-to-end tests (8, 6)	4m 45s
Thanos end-to-end tests (8, 7)	4m 17s
	1h 2m 20s

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