Refactor GitLab Dedicated and Self-Managed plans by plan type in config

Problem

Follow up from this discussion https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/12122#note_2393562285

The current structure of Dedicated and Self-Managed plans in (dedicated and self_managed nodes in config/application.yml) has been become challenging to parse in app/models/plan.rb as there is a growing list of variants: ecosystem, US public sector, duo with amazon q, etc.

Maintainability of these SKUs could be further improved by restructuring the dedicated and self_managed nodes in application.yml to use a nested key for each Dedicated / SM plan type e.g.

dedicated:
    ecosystem:
    us_pubsec:
        ecosystem:
    duo_with_amazon_q:
        ecosystem:

With this structure, the plans can be more readily accessed in plan.rb by variant/type:

• APP_CONFIG.zuora.plans.dedicated
• APP_CONFIG.zuora.plans.dedicated.ecosystem
• APP_CONFIG.zuora.plans.dedicated.us_pubsec
• etc

Proposal

Refactor dedicated and self_managed node in config/application.yml to use a nested/child key for each plan type, use this nested structure to parse dedicated plans in plan.rb.

Result

Improved maintainability of plans across application/yml and plan.rb.