Allow Dedicated customers to customize maximum instance-level CI/CD variable count
<!-- This template is a great use for issues that are feature::additions or technical tasks for larger issues.--> ### Proposal <!-- Use this section to explain the feature and how it will work. It can be helpful to add technical details, design proposals, and links to related epics or issues. --> <!-- Consider adding related issues and epics to this issue. You can also reference the Feature Proposal Template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20proposal%20-%20detailed.md) for additional details to consider adding to this issue. Additionally, as a data oriented organization, when your feature exits planning breakdown, consider adding the `What does success look like, and how can we measure that?` section. --> Currently, GitLab Dedicated customers are limited to 25 instance-level CI/CD variables. Self-managed customers can change this limit via a Rails console command, but Dedicated customers do not have access to do so. I'm requesting that we add support for modifying this setting via the UI and/or API so that Dedicated customers who need more variables can make the necessary changes. ## Implementation Table <!-- _NOTE: Use this to indicate all dependent issues related to this one which are required for launch._ --> | Group | Issue Link | | ------ | ------ | | ~backend | [Backend: Allow Dedicated customers to customize maximum instance-level CI/CD variable count](https://gitlab.com/gitlab-org/gitlab/-/issues/458023) | | ~frontend | :point_left: You are here | | ~documentation | [Documentation: Allow Dedicated customers to customize maximum instance-level CI/CD variable count](https://gitlab.com/gitlab-org/gitlab/-/issues/458027) | | Instrumentation | [Issue Title](url) |
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