Move Agent GraphQL types and resolvers to core

What does this MR do and why?

Part of making Cluster Agents available in Core (&6290 (closed)).

Moves Cluster Agent GraphQL types, resolvers and policies to core, removing license checks where applicable.

These changes are not yet reflected in any Core UI, however they will become available via the GraphQL API. This isn't a concern, as Agent records in Core will not be functional until various other services and APIs are moved.

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MR acceptance checklist

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#340355 (closed)