Update CHANGELOG.md for 12.8.0

[ci skip]

changelogs/unreleased/MaxWinterstein-master-patch-60978.yml

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-title: Add optional angle brackets in address_regex
-merge_request: 23797
-author: Max Winterstein
-type: fixed

changelogs/unreleased/Refactor-gl_dropdown-js.yml

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-title: refactoring gl_dropdown.js to use ES6 classes instead of constructor functions
-merge_request: 20488
-author: nuwe1
-type: other

changelogs/unreleased/Remove-addMultipleIssues-function-logic-from-list-js.yml

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-title: removes store logic from issue board models
-merge_request: 21404
-author: nuwe1
-type: other

changelogs/unreleased/Remove-save-function-logic-from-list-js.yml

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-title: removes store logic from issue board models
-merge_request: 21391
-author: nuwe1
-type: other

changelogs/unreleased/Updated-new-edit-wiki-page-to-equal-ui-elements.yml

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-title: Updated ui elements in wiki page creation
-merge_request: 25197
-author: Marc Schwede
-type: other

changelogs/unreleased/ab-projects-api-remove-unneeded-indexes.yml

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-title: Remove unneeded indexes on projects table
-merge_request: 24086
-author:
-type: performance

changelogs/unreleased/ab-projects-without-feature.yml

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-title: Ensure all Project records have a corresponding ProjectFeature record
-merge_request: 23766
-author:
-type: fixed

changelogs/unreleased/ab-tie-breaker-order.yml

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-title: Let tie breaker order follow primary sort direction (API)
-merge_request: 22795
-author:
-type: changed

changelogs/unreleased/add-extra-fields-to-the-application-context.yml

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-title: Add extra fields to the application context
-merge_request: 22792
-author:
-type: added

changelogs/unreleased/admin_user_memberships_endpoint.yml

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-title: Add users memberships endpoints for admins
-merge_request: 22518
-author:
-type: added

changelogs/unreleased/ag-addjson-log-to-admin-logs.yml

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-title: Replace unstructured application logs with structured (JSON) application logs in the admin interface
-merge_request: 24614
-author:
-type: other

changelogs/unreleased/ak-bump-retention.yml

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-title: Extend logs retention to period from 15 to 30 days
-merge_request: 24466
-author:
-type: changed

changelogs/unreleased/ak-drop-etag.yml

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-title: Drop etag cache on logs API
-merge_request: 24864
-author:
-type: fixed

changelogs/unreleased/ak-fix-alert.yml

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-title: Fix k8s logs alert display state
-merge_request: 24802
-author:
-type: fixed

changelogs/unreleased/ak-fix-logs-etag.yml

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-title: Fix logs api etag issues with elasticsearch
-merge_request: 23249
-author:
-type: fixed

changelogs/unreleased/ak-migration-cleanu.yml

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-title: Remove kibana_hostname column from clusters_applications_elastic_stacks table
-merge_request: 23503
-author:
-type: changed

changelogs/unreleased/ak-remove-es-ff.yml

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-title: Add new Elastic Stack cluster application for pod log aggregation
-merge_request: 23058
-author:
-type: added

changelogs/unreleased/ak-wait-for-green-es.yml

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-title: Wait for elasticsearch to be green on install
-merge_request: 24489
-author:
-type: added

changelogs/unreleased/al-196720-remove-destroy_user_associations_in_batches-ff.yml

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-title: Destroy user associations in batches like we do with projects
-merge_request: 24641
-author:
-type: performance

changelogs/unreleased/al-55240-access-policy-check-for-new-snippet-button.yml

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-title: Ensure New Snippet button is displayed based on the :create_snippet permission
-  in Project Snippets page and User profile > Snippets tab
-merge_request: 55240
-author:
-type: fixed