Update OpenAPI yaml file

What does this MR do and why?

It updates the OpenAPI with the following endpoints:

• API::AccessRequests
• API::Admin::BatchedBackgroundMigrations
• API::Admin::Ci::Variables
• API::Admin::InstanceClusters
• API::Admin::PlanLimits
• API::AlertManagementAlerts
• API::Appearance
• API::Applications
• API::Avatar
• API::Badges
• API::Branches
• API::BroadcastMessages
• API::BulkImports

Update OpenAPI yaml file

Changelog: changed

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