Update CHANGELOG.md for 12.0.0

[ci skip]

changelogs/unreleased/59376-Report-abuse-to-GitLab-should-be-Report-abuse-in-non-gitlab-com-instances.yml

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-title: Change "Report abuse to GitLab" to more generic wording
-merge_request: 28884
-author: Marc Schwede
-type: other

changelogs/unreleased/59587-add-graphql-logging.yml

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-title: Add dedicated logging for GraphQL queries
-merge_request: 27885
-author:
-type: other

changelogs/unreleased/59651-remove-unnecessary-decimal-places-on-chart-axes.yml

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-title: Remove unnecessary decimals on Metrics chart axis
-merge_request: 29468
-author:
-type: fixed

changelogs/unreleased/59987-move-sign-in-2fa-on-users-sign_in-above-intro-content-on-mobile.yml

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-title: Prioritize login form on mobile breakpoint
-merge_request: 28360
-author:
-type: changed

changelogs/unreleased/60034-default-web-ide-s-merge-request-checkbox-to-true.yml

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-title: Default MR checkbox to true in most cases
-merge_request: !28665
-author:
-type: changed

changelogs/unreleased/60180-jira-service-fix-nil-on-find-call.yml

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-title: 'Resolved JIRA service: NoMethodError: undefined method ''find'' for nil:NilClass'
-merge_request: 28206
-author:
-type: fixed

changelogs/unreleased/60250-remove-mr_push_options-flag.yml

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-title: Remove the mr_push_options feature flag
-merge_request: 28278
-author:
-type: changed

changelogs/unreleased/60303-replace-sidekiq-mtail-metrics.yml

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-title: Replaces sidekiq mtail metrics with ruby instrumentation metrics
-merge_request: 29215
-author:
-type: changed

changelogs/unreleased/60323-inline-validation-for-users-name-and-username-length.yml

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-title: Update registration form to indicate invalid name or username length on input
-merge_request: 28095
-author: Jiaan Louw
-type: changed

changelogs/unreleased/60379-remove-ci-preparing-state-feature-flag.yml

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-title: Remove ability for group clusters to be automatically configured on creation
-merge_request: 27245
-author:
-type: removed

changelogs/unreleased/60425-fix-500-when-accessing-charts-with-anonymous-user.yml

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-title: "Fix 500 error when accessing charts with an anonymous user"
-merge_request: 28091
-author: Diego Silva
-type: fixed

changelogs/unreleased/60617-allow-switching-from-gitlab-managed-to-unmanaged-clusters.yml

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-title: Allow switching clusters between managed and unmanaged
-merge_request: 29322
-author:
-type: added

changelogs/unreleased/60750-milestone-header.yml

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-title: Fix layout of group milestone header
-merge_request:
-author:
-type: fixed

changelogs/unreleased/60818_yamllint_project_root.yml

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-title: Fix yaml linting for project root *.yml files
-merge_request: 27579
-author: Will Hall
-type: fixed

changelogs/unreleased/60819_yamllint_gitlabci.yml

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-title: Fix yaml linting for GitLab CI inside project (.gitlab/ci) *.yml files and CI template files
-merge_request: 27576
-author: Will Hall
-type: fixed

changelogs/unreleased/609120-ref-link.yml

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-title: Fixes Ref link being displayed as raw HTML in the Pipelines page
-merge_request: 28823
-author:
-type: fixed

changelogs/unreleased/60987-emoji-picker-popup.yml

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-title: Fix emoji picker visibility issue
-merge_request: 28984
-author:
-type: fixed

changelogs/unreleased/61024-update-resolved-icon.yml

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-title: Add check circle filled icon for resolved comments
-merge_request: 28663
-author: 
-type: changed

changelogs/unreleased/6104-ee-ce-difference.yml

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-title: Unified EE/CS differences in repository/show.html
-merge_request: 13562
-author:
-type: other

changelogs/unreleased/61045-charts-with-many-overlapping-series-display-incorrectly.yml

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-title: Eliminate color inconsistencies in metric graphs
-merge_request: 29127
-author:
-type: fixed