Make workspace agent config types alpha

What does this MR do and why?

In the previous release, we added two types to the GraphQL API which should have been marked alpha but were not.

Even though the GraphQL Style Guide indicates that items should not be retroactively marked alpha, we would like to make an exception in this case, for the following reasons:

1. They were only added in the previous release - MRs adding them were merged in 17.4 (Add agent config type, resolve, finder with per... (!158587 - merged) and Migrate remote_development_agent_configs table (!163846 - merged))
2. Nothing in the app currently depends on these types. They were added to facilitate work which since been deprioritized, and to provide completeness of the GraphQL API with respect to the underlying models.
3. There is a very low (likely zero) likelihood that any end users are using these fields already, given the currently low usage of the feature overall, and this config data specifically (based on .com DB contents, Service Ping metrics, and direct contact with multiple enterprise customers evaluating the feature).
   • SaaS/.com: See metrics in internal note below
   • Self-hosted: MAU metrics for SaaS and Self-Managed: https://10az.online.tableau.com/t/gitlab/views/EditorMetrics/WorkspacesDashboard
4. There is much ongoing and upcoming work and iteration around these types and their fields, much of which involves adding, evolving, and removing fields from these types. Having to observe the normal 6-month deprecation period around these types will make that work significantly more difficult and error-prone. Examples:
   • Workspace Suspension with Delayed Termination (gitlab-org#14910 - closed)
   • Sudo access in a workspace (&13983 - closed)
   • Support building and running containers in a wo... (&11319 - closed)

Note that remoteDevelopmentAgentConfig has been changed from deprecated to alpha. This intentional This is because it was renamed due to the category rename from ~Category:Remote Development to Category:Workspaces. Both of these types point to the same underlying table (workspaces_agent_configs), so the same data is still available through both of them. But by making remoteDevelopmentAgentConfig to be alpha, it means we can go ahead and delete it (and all associated fields/code) now, without waiting 6 months until %17.10

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

No UI or functionality changes, only GraphQL API doc changes.

How to set up and validate locally

See that fields are marked "Experimental" in the GraphQL docs.