compactor depends on memberlist for memberlist ring option

[trevorwhitney]

What this PR does / why we need it:

We seem to have introduced a race condition when using memberlist for the compactor ring:

│ level=info ts=2021-11-03T23:26:34.317080539Z caller=main.go:94 msg="Starting Loki" version="(version=k70-07ea1ed, branch=k70, revision=07ea1ed99)"          ││ level=info ts=2021-11-03T23:26:34.317342925Z caller=server.go:260 http=[::]:3100 grpc=[::]:9095 msg="server listening on addresses"                         ││ panic: runtime error: invalid memory address or nil pointer dereference                                                                                     ││ [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xed5498]                                                                                      ││ goroutine 1 [running]:                                                                                                                                      ││ github.com/grafana/dskit/kv/memberlist.(*KVInitService).GetMemberlistKV(0x0)                                                                                ││     /src/loki/vendor/github.com/grafana/dskit/kv/memberlist/kv_init_service.go:57 +0x18                                                                     ││ github.com/grafana/dskit/kv.createClient({_, _}, {_, _}, {{{0x22456a8, 0xe}, {0x0, 0x0}, 0x4a817c800, 0x0, ...}, ...}, ...)                                 ││     /src/loki/vendor/github.com/grafana/dskit/kv/client.go:146 +0x4b2                                                                                       ││ github.com/grafana/dskit/kv.NewClient({{0x223da05, 0xa}, {0x223f2b3, 0xb}, {{{0x22456a8, 0xe}, {0x0, 0x0}, 0x4a817c800, 0x0, ...}, ...}, ...}, ...)         ││     /src/loki/vendor/github.com/grafana/dskit/kv/client.go:123 +0x11e                                                                                       ││ github.com/grafana/loki/pkg/storage/stores/shipper/compactor.NewCompactor({{0xc000501c10, 0xf}, {0x2231d26, 0x3}, {0x2235bc8, 0x6}, 0x8bb2c97000, 0x0, 0x68 ││     /src/loki/pkg/storage/stores/shipper/compactor/compactor.go:125 +0x33a                                                                                  ││ github.com/grafana/loki/pkg/loki.(*Loki).initCompactor(0xc000343500)                                                                                        ││     /src/loki/pkg/loki/modules.go:668 +0x1df                                                                                                                ││ github.com/grafana/dskit/modules.(*Manager).initModule(0xc00012d710, {0x7ffd92f27d0d, 0x1}, 0xc000245c50, 0xc00091cc18)                                     ││     /src/loki/vendor/github.com/grafana/dskit/modules/modules.go:106 +0x22c                                                                                 ││ github.com/grafana/dskit/modules.(*Manager).InitModuleServices(0xc000434a50, {0xc0007e6bb0, 0x1, 0x40ac5d})                                                 ││     /src/loki/vendor/github.com/grafana/dskit/modules/modules.go:78 +0x10c                                                                                  ││ github.com/grafana/loki/pkg/loki.(*Loki).Run(0xc000343500)                                                                                                  ││     /src/loki/pkg/loki/loki.go:284 +0x4b                                                                                                                    ││ main.main()                                                                                                                                                 ││     /src/loki/cmd/loki/main.go:96 +0xd70

This PR add MemberlistKV as a dependency of Compactor which should fix this.

[slim-bean]

LGTM