Update CHANGELOG.md for 12.8.0

[ci skip]

changelogs/unreleased/refactoring-entities-file-19.yml

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-title: Separate entities into own class files
-merge_request: 24941
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-2.yml

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-title: Refactor user entities into own class files
-merge_request: 23730
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-20.yml

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-title: Separate tag and release entities into own class files
-merge_request: 24943
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-21.yml

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-title: Separate job entities into own class files
-merge_request: 24948
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-22.yml

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-title: Separate entities into own class files
-merge_request: 24950
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-23.yml

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-title: Separate environment entities into own class files
-merge_request: 24951
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-24.yml

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-title: Separate token and template entities into own class files
-merge_request: 24955
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-25.yml

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-title: Separate token entities into own class files
-merge_request: 24974
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-26.yml

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-title: Separate JobRequest entities into own class files
-merge_request: 24977
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-27.yml

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-title: Separate entities into own class files
-merge_request: 24985
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-28.yml

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-title: Separate page domain entities into own class files
-merge_request: 24987
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-29.yml

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-title: Separate Application and Blob entities into own class files
-merge_request: 24997
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-3.yml

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-title: Add separate classes for user related entities for email, membership, status
-merge_request: 23748
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-30.yml

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-title: Separate badge entities into own class files
-merge_request: 25116
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-31.yml

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-title: Separate provider, platform and post receive entities into own class files
-merge_request: 25119
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-32.yml

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-title: Separate cluster entities into own class files
-merge_request: 25121
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-4.yml

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-title: Add separate classes for project hook, identity, export status
-merge_request: 23789
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-5.yml

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-title: Add separate classes for project related classes
-merge_request: 23887
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-6.yml

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-title: Separate project and group entities into own class files
-merge_request: 24070
-author: Rajendra Kadam
-type: added

changelogs/unreleased/refactoring-entities-file-7.yml

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-title: Separate commit entities into own class files
-merge_request: 24085
-author: Rajendra Kadam
-type: added