Move InstanceMetadata concerns under AppConfig context

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What does this MR do and why?

As a follow-up from !164806 (merged), in that MR we introduced the bounded context AppConfig. This commit moves some of these non-bounded modules into this domain. The modules that are moved under AppConfig concern InstanceMetadata.

• app/models/instance_metadata.rb should become AppConfig::ServerInfo.
• app/models/instance_metadata/kas.rb should become AppConfig::KasInfo.
• app/graphql/types/metadata_type.rb should become Types::AppConfig::ServerInfoType.
• app/graphql/resolvers/metadata_resolver.rb should become Resolvers::AppConfig::ServerInfoResolver.

I also fixed some of the Rubocop offenses in these files and therefore removed the corresponding entries from .rubocop_todo/**/*.

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I did not make UI changes.

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I only moved files. The pipeline should still succeed.

See also !164806 (comment 2087502138)
Related to #482810