Update CHANGELOG.md for 12.8.0

[ci skip]

changelogs/unreleased/193075-usage-ping-timing-out-for-larger-instances-batch.yml

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-title: Fix usage ping timeouts with batch counters
-merge_request: 22705
-author:
-type: performance

changelogs/unreleased/194164-add-missing-detailed-sentry-error-graphql.yml

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-title: Add tags, external_base_url, gitlab_issue to Sentry Detailed Error graphql
-merge_request: 23483
-author:
-type: added

changelogs/unreleased/194381-new-integrations-are-not-active-by-default.yml

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-title: Activate new project integrations by default
-merge_request: 23009
-author:
-type: changed

changelogs/unreleased/195137-update-compression-webpack-plugin-and-copy-webpack-plugin.yml

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-title: Update webpack related packages
-merge_request: 22456
-author: Takuya Noguchi
-type: security

changelogs/unreleased/195701-web-ide-dark-theme.yml

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-title: Dark syntax highlighting theme for Web IDE
-merge_request: 24158
-author:
-type: added

changelogs/unreleased/195888-import_to_find_group_objects_within_all_group_ancestors.yml

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-title: Search group-level objects among all ancestors during project import
-merge_request:
-author:
-type: changed

changelogs/unreleased/195989-quick-action-add-dup-assignee-error.yml

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-title: Fix error when assigning an existing asignee
-merge_request: 23416
-author:
-type: fixed

changelogs/unreleased/196070-move-mr-from-right-sidebar-to-bottom-bar.yml

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-title: Move Merge Request from right sidebar of Web IDE to bottom bar
-merge_request: 24746
-author:
-type: changed

changelogs/unreleased/196179-fixes-modal-button-spacing.yml

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-title: Fixes spacing issue in modal footers
-merge_request: 23327
-author:
-type: fixed

changelogs/unreleased/196183-convert-ci-cd-charts-to-echarts.yml

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-title: Migrate CI CD statistics + duration chart to VueJS
-merge_request: 23840
-author:
-type: changed

changelogs/unreleased/196183-convert-pipelines-last-week-chart-to-echarts.yml

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-title: Migrate CI CD pipelines charts to ECharts
-merge_request: 24057
-author:
-type: changed

changelogs/unreleased/196184-convert-insights-to-echarts.yml

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-title: Move insights charts to echarts
-merge_request: 24661
-author:
-type: other

changelogs/unreleased/196243-add-exclusive-guard.yml

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-title: Fix race condition bug in Prometheus managed app update process
-merge_request: 24228
-author:
-type: fixed

changelogs/unreleased/196250.yml

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-title: Remove N+1 query for profile notifications
-merge_request: 22845
-author: Ohad Dahan
-type: performance

changelogs/unreleased/196660-replace-underscore-with-lodash-for-app-assets-javascripts-mirrors.yml

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-title: Replace underscore with lodash for ./app/assets/javascripts/mirrors
-merge_request: 24967
-author: Jacopo Beschi @jacopo-beschi
-type: changed

changelogs/unreleased/196678-replace-_-with-lodash.yml

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-title: Replaced underscore with lodash for spec/javascripts/badges
-merge_request: 25135
-author: Shubham Pandey
-type: other

changelogs/unreleased/196690-replace-_-with-lodash.yml

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-title: Replaced underscore with lodash for spec/javascripts/vue_shared/components
-merge_request: 25018
-author: Shubham Pandey
-type: other

changelogs/unreleased/196765-bump-ingress-to-1-29.yml

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-title: Bump ingress managed app chart to 1.29.3
-merge_request: 23461
-author:
-type: changed

changelogs/unreleased/196777-add-account-creation-and-sign-in-ip-to-api.yml

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-title: Expose current and last IPs to /users endpoint
-merge_request: 19781
-author:
-type: added

changelogs/unreleased/196797-blob-content.yml

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-title: Refactored snippets view to Vue
-merge_request: 25188
-author:
-type: other