mimirtool: fail on duplicate rules with --strict

[colega]

What this PR does

Changes the behaviour of mimirtool rules check to fail on duplicated rules when --strict is provided.

Also changed the output to use the logger instead of fmt, and added a test.

The output looks like this (on main before #5023 was merged):

$ go run ./cmd/mimirtool rules check --strict --rule-dirs ./operations/mimir-mixin-compiled
ERRO[0000] duplicate rules found                         duplicate_rules=2 error="rules should emit unique series, to avoid producing inconsistencies while recording expressions" namespace=alerts
ERRO[0000] duplicate rule                                label[severity]=warning metric=MimirRolloutStuck namespace=alerts
ERRO[0000] duplicate rule                                label[severity]=critical metric=MimirCompactorHasNotUploadedBlocks namespace=alerts
mimirtool: error: 2 duplicate rules found in namespace "alerts", try --help
exit status 1

Which issue(s) this PR fixes or relates to

Relates to #5023

Checklist

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

[aknuds1]

The implementation looks solid, but there are some minor issues with the tests.

[colega]

Thank you for your review, @aknuds1, the comments should be addressed now.

[aknuds1]

LGTM, thanks for addressing my feedback!