Update CHANGELOG.md for 12.8.0

[ci skip]

changelogs/unreleased/search-scope-blobs-fix.yml

----
-title: Fix blobs search API degradation
-merge_request: 24607
-author:
-type: fixed

changelogs/unreleased/selective-geo-sync.yml

----
-title: Add selective sync support to Geo Nodes API update endpoint
-merge_request: 22828
-author: Rajendra Kadam
-type: added

changelogs/unreleased/selective-sync-params-create-geo.yml

----
-title: Add selective sync support to Geo Nodes API create endpoint
-merge_request: 23729
-author: Rajendra Kadam
-type: added

changelogs/unreleased/self-monitoring-env.yml

----
-title: Create an environment for self monitoring project
-merge_request: 24403
-author:
-type: added

changelogs/unreleased/sh-add-due-date-simple-sort.yml

----
-title: Optimize issue search when sorting by due date and position
-merge_request: 24217
-author:
-type: performance

changelogs/unreleased/sh-add-weight-simple-sort.yml

----
-title: Optimize issue search when sorting by weight
-merge_request: 24208
-author:
-type: performance

changelogs/unreleased/sh-bump-pg-gem-1-2-2.yml

----
-title: Update pg gem to v1.2.2
-merge_request: 23237
-author:
-type: other

changelogs/unreleased/sh-fix-current-settings.yml

----
-title: Fix application settings not working with pending migrations
-merge_request:
-author:
-type: fixed

changelogs/unreleased/sh-fix-empty-namespace-git-access.yml

----
-title: Eliminate statement timeouts when namespace is blank
-merge_request: 23839
-author:
-type: fixed

changelogs/unreleased/sh-fix-mermaid-releases-page.yml

----
-title: Fix Markdown not rendering on releases page
-merge_request: 23370
-author:
-type: fixed

changelogs/unreleased/sh-fix-squash-one-commit.yml

----
-title: Skip squashing with only one commit in a merge request
-merge_request: 23744
-author:
-type: fixed

changelogs/unreleased/sh-optimize-archive-controller-ref-names.yml

----
-title: Optimize ref name lookups in archive downloads
-merge_request: 23890
-author:
-type: performance

changelogs/unreleased/sh-optimize-runners-admin-show.yml

----
-title: Optimize page loading of Admin::RunnersController#show
-merge_request: 23309
-author:
-type: performance

changelogs/unreleased/sh-promote-stackprof.yml

----
-title: Promote stackprof into a production gem
-merge_request: 24564
-author:
-type: other

changelogs/unreleased/sh-reduce-gitaly-calls-submodules.yml

----
-title: Eliminate Gitaly N+1 queries loading submodules
-merge_request: 23292
-author:
-type: performance

changelogs/unreleased/sh-revert-prometheus-application-migration.yml

----
-title: Clean backgroud_migration queue from ActivatePrometheusServicesForSharedCluster
-  jobs.
-merge_request: 24135
-author:
-type: fixed

changelogs/unreleased/sh-sanitize-api-request-parameters.yml

----
-title: Sanitize request parameters in exceptions_json.log
-merge_request: 24625
-author:
-type: fixed

changelogs/unreleased/sh-sanitize-pipeline-params.yml

----
-title: Redact push options from error logs
-merge_request: 24540
-author:
-type: fixed

changelogs/unreleased/sh-squelch-snowplow-tracker-messages.yml

----
-title: Squelch Snowplow tracker log messages
-merge_request: 24809
-author:
-type: fixed

changelogs/unreleased/sh-trim-extra-periods-merge-error.yml

----
-title: Trim extra period when merge error displayed
-merge_request: 23737
-author:
-type: fixed