Update CHANGELOG.md for 10.4.0

[ci skip]

changelogs/unreleased/remove-incorrect-guidance.yml

----
-title: Removed incorrect guidance stating blocked users will be removed from groups
-  and project as members
-merge_request: 15947
-author: CesarApodaca
-type: fixed

changelogs/unreleased/remove-links-mr-empty-state.yml

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-title: Remove related links in MR widget when empty state
-merge_request:
-author:
-type: fixed

changelogs/unreleased/remove-soft-removals.yml

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-title: Remove soft removals related code
-merge_request: 15789
-author:
-type: changed

changelogs/unreleased/remove-tabindexes-from-tag-form.yml

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-title: removed tabindexes from tag form
-merge_request:
-author: Marcus Amargi
-type: changed

changelogs/unreleased/sh-add-schedule-pipeline-run-now.yml

----
-title: Add button to run scheduled pipeline immediately
-merge_request:
-author:
-type: added

changelogs/unreleased/sh-catch-invalid-uri-markdown.yml

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-title: Gracefully handle garbled URIs in Markdown
-merge_request:
-author:
-type: fixed

changelogs/unreleased/sh-fix-bare-import-hooks.yml

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-title: Fix hooks not being set up properly for bare import Rake task
-merge_request:
-author:
-type: fixed

changelogs/unreleased/sh-fix-mermaid-start-on-load-typo.yml

----
-title: Fix Mermaid drawings not loading on some browsers
-merge_request:
-author:
-type: fixed

changelogs/unreleased/sh-make-kib-human.yml

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-title: Humanize the units of "Showing last X KiB of log" in job trace
-merge_request:
-author:
-type: fixed

changelogs/unreleased/sh-optimize-commit-stats.yml

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-title: Speed up generation of commit stats by using Rugged native methods
-merge_request:
-author:
-type: performance

changelogs/unreleased/sh-validate-path-project-import.yml

----
-title: Avoid leaving a push event empty if payload cannot be created
-merge_request:
-author:
-type: fixed

changelogs/unreleased/show-inline-edit-btn.yml

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-title: Move edit button to second row on issue page (and change it to a pencil icon)
-merge_request:
-author:
-type: changed

changelogs/unreleased/show_proper_labels_in_board_issue_sidebar_when_issue_is_closed.yml

----
-title: show None when issue is in closed list and no labels assigned
-merge_request: 15976
-author: Christiaan Van den Poel
-type: fixed

changelogs/unreleased/sophie-h-gitlab-ce-patch-15.yml

----
-title: Hide link to issues/MRs from labels list if issues/MRs are disabled.
-merge_request: 15863
-author: Sophie Herold
-type: fixed

changelogs/unreleased/tc-correct-email-in-reply-to.yml

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-title: Make mail notifications of discussion notes In-Reply-To of each other
-merge_request: 14289
-author:
-type: changed

changelogs/unreleased/update-redis-rack.yml

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-title: Update redis-rack to 2.0.4
-merge_request:
-author:
-type: other

changelogs/unreleased/winh-modal-target-id.yml

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-title: Add id to modal.vue to support data-toggle="modal"
-merge_request: 16189
-author:
-type: other

changelogs/unreleased/winh-translate-contributors-page-dates.yml

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-title: Translate date ranges on contributors page
-merge_request: 15846
-author:
-type: changed