Enable `admin_deploy_keys_vue` feature flag by default

What does this MR do and why?

Enables the admin_deploy_keys_vue feature flag by default. This will cause the Admin -> Deploy keys view to be renderd with Vue instead of HAML. The deploy keys will be lazy loaded via an API request and this also adds pagination (which was previously not implemented).

Feature has been rolled out and verified on GitLab.com #344855 (closed)

Screenshots or screen recordings

Before

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After

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How to set up and validate locally

1. Fire up the Rails console
   • bin/rails console
2. Create some deploy keys

50.times do
    project = Project.order("RANDOM()").first
    deploy_key = FactoryBot.create(:deploy_key, public: true)
    FactoryBot.create(:deploy_keys_project, :write_access, deploy_key: deploy_key, project: project)
end

1. Sign in as an Admin and navigate to /admin/deploy_keys

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #344855 (closed)