Update CHANGELOG.md for 9.1.0

[ci skip]

changelogs/unreleased/29550-fix-quick-submit-on-preview.yml

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-title: Fix quick submit short-cut on preview tab for comments
-merge_request: 10002
-author:

changelogs/unreleased/29555-align-all-todo.yml

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-title: align Mark all as done with other Done buttons on Todos page
-merge_request:
-author:

changelogs/unreleased/29575-polling.yml

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-title: Adds polling utility function for vue resource
-merge_request:
-author:

changelogs/unreleased/29662-allow-unauthenticated-branches-api.yml

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-title: Allow unauthenticated access to some Branch API GET endpoints
-merge_request:
-author:

changelogs/unreleased/29669-redirect-referer-params.yml

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-title: Fix redirection after login when the referer have params
-merge_request:
-author: mhasbini

changelogs/unreleased/29670-jira-integration-documentation-improvment.yml

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-title: Added clarification to the Jira integration documentation.
-merge_request: 10066
-author: Matthew Bender

changelogs/unreleased/29828-change-search-hint-in-new-filters.yml

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-title: Change hint on first row of filters dropdown to `Press Enter or click to search`
-merge_request: 10138
-author:

changelogs/unreleased/29830-build-scroll-indicator.yml

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-title: fix sidebar padding for build and wiki pages
-merge_request:
-author:

changelogs/unreleased/29843-project-subgroup-transfer.yml

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-title: Correctly update paths when changing a child group
-merge_request:
-author:

changelogs/unreleased/2989-run-cicd-pipelines-on-a-schedule-idea1-basic-backend-implementation.yml

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-title: Resolve "Run CI/CD pipelines on a schedule" - "Basic backend implementation"
-merge_request: 10133
-author: dosuken123

changelogs/unreleased/29897-remove-force-scroll-for-mr-changes-diff.yml

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-title: Remove forced scroll into view when switching to Changes MR tab
-merge_request:
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changelogs/unreleased/29929-jira-doc.yml

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-title: Fix link to Jira service documentation
-merge_request:
-author:

changelogs/unreleased/29930-fix-profile-cover-button-a11y.yml

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-title: Add tooltip and accessibility for profile cover buttons
-merge_request: 10182
-author:

changelogs/unreleased/29950-vue-pagination-icons.yml

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-title: consistent icons in vue and kaminari pagers
-merge_request:
-author:

changelogs/unreleased/30008-textarea-focus.yml

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-title: refocus textarea after attaching a file
-merge_request:
-author:

changelogs/unreleased/30021-api-deploy_keys-can_push-is-not-honoured.yml

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-title: Enable creation of deploy keys with write access via the API
-merge_request:
-author:

changelogs/unreleased/30056-rename-milestones-empty.yml

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-title: Removed Milestone#is_empty?
-merge_request: 10523
-author: Jacopo Beschi @jacopo-beschi

changelogs/unreleased/30112-fix-pipelines-sub-nav-highlight.yml

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-title: Fix sub-nav highlighting for `Environments` and `Jobs` pages
-merge_request: 10254
-author:

changelogs/unreleased/30125-markdown-security.yml

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-title: Remove the class attribute from the whitelist for HTML generated from Markdown.
-merge_request:
-author:

changelogs/unreleased/30195-document-search-param-on-api.yml

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-title: Add search optional param and docs for V4
-merge_request:
-author: