Update CHANGELOG.md for 9.0.0

[ci skip]

changelogs/unreleased/26900-pipelines-tabs.yml

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-title: Adds Pending and Finished tabs to pipelines page
-merge_request:
-author:

changelogs/unreleased/26957-tanuki-anim-hang.yml

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-title: don't animate logo when downloading files
-merge_request:
-author:

changelogs/unreleased/27032-add-a-house-keeping-api-call.yml

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-title: Add housekeeping endpoint for Projects API
-merge_request: 9421
-author:

changelogs/unreleased/27142-api-replace-destroy-with-stop-environment.yml

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-title: 'API: Add environment stop action'
-merge_request: 8808
-author:

changelogs/unreleased/27287-label-dropdown-error-messages.yml

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-title: Fix displaying error messages for create label dropdown
-merge_request: 9058
-author: Tom Koole

changelogs/unreleased/27336-add-environment-url-link-to-terminal-page.yml

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-title: Added external environment link to web terminal view
-merge_request: 8303
-author:

changelogs/unreleased/27354-navigation-new-button.yml

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-title: Re-add the New Project button in nav bar
-merge_request:
-author:

changelogs/unreleased/27376-cache-default-branch-pipeline-on-project.yml

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-title: Speed up project dashboard by caching pipeline status and eager loading routes
-merge_request: 9903
-author:

changelogs/unreleased/27452-update-issue-count.yml

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-title: update issue count when closing/reopening an issue
-merge_request:
-author:

changelogs/unreleased/27501-api-use-visibility-everywhere.yml

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-title: "API: Use `visibility` as string parameter everywhere"
-merge_request: 9337
-author:

changelogs/unreleased/27520-option-to-prevent-signing-in-from-multiple-ips.yml

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-title: Option to prevent signing in from multiple ips
-merge_request: 8998
-author:

changelogs/unreleased/27523-make-stuck-build-detection-more-performant.yml

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-title: Make stuck builds detection more performant
-merge_request: 9025
-author:

changelogs/unreleased/27530-fix-job-dropdown-pipeline-console-error.yml

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-title: Fixes job dropdown action throws error in js console
-merge_request: 9182
-author:

changelogs/unreleased/27532_api_changes.yml

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-title: Use iids as filter parameter
-merge_request: 9096
-author:

changelogs/unreleased/27568-refactor-very-slow-dropdown-asignee-spec.yml

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-title: Refactor dropdown_assignee_spec
-merge_request: 9711
-author: George Andrinopoulos

changelogs/unreleased/27608-fixes-markdown-in-activity-feed-is-light-gray.yml

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-title: Fixes markdown in activity-feed is gray
-merge_request: 9179
-author:

changelogs/unreleased/27610-issue-number-alignment.yml

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-title: fixes issue number alignment problem in MR and issue list
-merge_request: 9020
-author:

changelogs/unreleased/27631-fix-small-height-of-activity-header-page.yml

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-title: "Fix small height of activity header page"
-merge_request: 8952
-author: Pavel Sorokin

changelogs/unreleased/27726-fix-dropdown-width-in-admin-project-page.yml

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-title: Fixes dropdown width in admin project page
-merge_request: 9002
-author:

changelogs/unreleased/27762-add-default-artifacts-expiration.yml

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-title: Add admin setting for default artifacts expiration
-merge_request: 9219
-author: