Remove APIEnableRulesBackup config and use Ring.ReplicationFactor ins…

[emanlodovice]

…tead

What this PR does:
This PR removes the -experimental.ruler.api-enable-rules-backup config because it only makes sense if ruler.ring.replication-factor is set to a value greater than 1. So instead of having the a dedicated config we just infer that rules backup is enabled if ruler.ring.replication-factor is greater than 1.

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[yeya24]

Test failed related to minimize spread token, unrelated but worth taking a look. @alanprot

--- FAIL: TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy (34.36s)
    --- FAIL: TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy/num_instances_=_60,_num_zones_=_3,_stable_sharding_=_true (0.10s)
        ring_test.go:2446: random generator seed: 1714124452728006355
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x16f8a95]

goroutine 679 [running]:
testing.tRunner.func1.2({0x18fb9e0, 0x36fb220})
	/usr/local/go/src/testing/testing.go:1545 +0x3f7
testing.tRunner.func1()
	/usr/local/go/src/testing/testing.go:1548 +0x716
panic({0x18fb9e0?, 0x36fb220?})
	/usr/local/go/src/runtime/panic.go:[92](https://github.com/cortexproject/cortex/actions/runs/8846062636/job/24291178688?pr=5901#step:6:93)0 +0x270
github.com/cortexproject/cortex/pkg/ring.(*MinimizeSpreadTokenGenerator).GenerateTokens(0xc002ece750, 0xc0001df580, {0xc000015f65, 0xb}, {0xc000015f7a, 0x6}, 0x80, 0x1)
	/__w/cortex/cortex/pkg/ring/token_generator.go:131 +0xab5
github.com/cortexproject/cortex/pkg/ring.TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy.func1(0xc005be5380)
	/__w/cortex/cortex/pkg/ring/ring_test.go:2495 +0xe83
testing.tRunner(0xc005be5380, 0xc002bc9500)
	/usr/local/go/src/testing/testing.go:1595 +0x262
created by testing.(*T).Run in goroutine 6[94](https://github.com/cortexproject/cortex/actions/runs/8846062636/job/24291178688?pr=5901#step:6:95)
	/usr/local/go/src/testing/testing.go:1648 +0x846
FAIL	github.com/cortexproject/cortex/pkg/ring	738.167s

[yeya24]

Love this change. Great work. Thanks @emanlodovice!