Update CHANGELOG.md for 12.9.0

[ci skip]

changelogs/unreleased/208889-optimize-event-counters.yml

----
-title: Optimize event counters query performance in usage data
-merge_request: 26444
-author:
-type: performance

changelogs/unreleased/208890-optimize-notes-counters.yml

----
-title: Optimize notes counters in usage data
-merge_request: 26871
-author:
-type: performance

changelogs/unreleased/208891-optimize-todos-counters.yml

----
-title: Optimize todos counters in usage data
-merge_request: 26442
-author:
-type: performance

changelogs/unreleased/208914-crud-for-instance-level-integrations.yml

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-title: Add CRUD for Instance-Level Integrations
-merge_request: 26454
-author:
-type: added

changelogs/unreleased/208923-enable-batch-counting-for-some-individual-queries.yml

----
-title: Optimize clusters counters query performance in usage data
-merge_request: 26887
-author:
-type: performance

changelogs/unreleased/208936.yml

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-title: update table layout for error tracking list on medium view ports
-merge_request: 26479
-author:
-type: other

changelogs/unreleased/209002-change-evidence-sha-clipboard-button-hover-text.yml

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-title: Fix evidence SHA clipboard hover text.
-merge_request: 26608
-author: Gilang Gumilar
-type: fixed

changelogs/unreleased/209207-spinner-appears-to-be-broken.yml

----
-title: Fix spinner in Create MR dropdown
-merge_request: 26679
-author:
-type: fixed

changelogs/unreleased/209277-introduce-a-feature-flag-for-resolve-notifications-for-when-pipeli.yml

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-title: Introduce a feature flag for Notifications for when pipelines are fixed
-merge_request: 26682
-author: Jacopo Beschi @jacopo-beschi
-type: changed

changelogs/unreleased/209761-fix-wiki-directories-with-hyphens.yml

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-title: Fix WikiPage#title_changed for paths with spaces
-merge_request: 27087
-author:
-type: fixed

changelogs/unreleased/209783-follow-up-from-resolve-notifications-for-when-pipelines-are-fixed.yml

----
-title: Correctly send notification on pipeline retry
-merge_request: 26803
-author: Jacopo Beschi @jacopo-beschi
-type: fixed

changelogs/unreleased/210007-optimize-services_usage-counters.yml

----
-title: Optimize services usage counters using batch counters
-merge_request: 26973
-author:
-type: performance

changelogs/unreleased/210008-the-same-chart-appears-twice-for-different-embeds.yml

----
-title: Fix embeds so that a chart appears only once
-merge_request: 26997
-author:
-type: fixed

changelogs/unreleased/210051-optimize-or-remove-ldap_users-counter.yml

----
-title: Optimize members counters query performance in usage data
-merge_request: 27197
-author:
-type: performance

changelogs/unreleased/210332-approximate-counters-are-not-working-on-gitlab-com.yml

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-title: Use batch counters instead of approximate counters in usage data
-merge_request: 27218
-author:
-type: performance

changelogs/unreleased/210335-fix-handling-of-numeric-emoji-names.yml

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-title: Fix backend validation of numeric emoji names
-merge_request: 27101
-author:
-type: fixed

changelogs/unreleased/21765-group-token-refactor.yml

----
-title: Addition of the Group Deploy Token interface
-merge_request: 24102
-author:
-type: added

changelogs/unreleased/21811-group-create-deploy-tokens.yml

----
-title: Add api endpoint for creating group deploy tokens
-merge_request: 25629
-author:
-type: added

changelogs/unreleased/21811-group-delete-deploy-token.yml

----
-title: Add API endpoint for deleting group deploy tokens
-merge_request: 25222
-author:
-type: added

changelogs/unreleased/21811-group-list-deploy-tokens.yml

----
-title: Add api endpoint for listing deploy tokens for a group
-merge_request: 25219
-author:
-type: added