Docs: Correct AiUserMetrics and AiMetrics offering badges to include self-managed

Problem to solve

The GraphQL API docs for Duo and SDLC Trends show offering badges of "GitLab.com, GitLab Dedicated" for AiUserMetrics and AiMetrics. This is incorrect — source code confirms no offering restriction exists for self-managed instances.

Source verification: The resolvers at ee/app/graphql/resolvers/analytics/ai/ do not check Gitlab::CurrentSettings.should_check_namespace_plan? or any offering gate. Self-managed instances with ClickHouse configured can use these APIs.

The stale badges cause self-managed administrators to skip these APIs, believing they are unavailable on their deployment type.

Further details

Affected docs:

• doc/api/graphql/duo_and_sdlc_trends.md — Offering badges for AiUserMetrics and AiMetrics sections

Audience: Self-managed administrators measuring Duo adoption via GraphQL.

Proposal

Update the offering badges for AiUserMetrics and AiMetrics from "GitLab.com, GitLab Dedicated" to "GitLab.com, GitLab Self-Managed, GitLab Dedicated".