Remove connection types from CI lint mutation

What does this MR do and why?

Linting a CI config returns a Ruby hash, not ActiveRecord objects. We don't need to have the overhead of connection types for presenting the hash data.

This MR:

• Creates Ci::ConfigType to be the CiConfigV2. We don't need to nest it as Ci::Config::ConfigType because Config is used redundantly
• Creates a LegacyConfig module to use the code that can be deleted when we remove QueryType.ciConfig
• Does not rename the graphql_name for the legacy types because that would be a breaking change. Instead the new types have graphql_name appended with V2
• Removes the WIP ci_lint_mutation feature flag
• Deprecates the QueryType.ciConfig field

Issue: Backend: Graphql mutation for CI Lint (#540764 - closed)