Move GitlabSubscriptionHistory to GitlabSubscriptions::SubscriptionHistory

What does this MR do and why?

This is the first of a series of MRs to implement https://gitlab.com/gitlab-org/gitlab/-/issues/355985 as part of https://gitlab.com/groups/gitlab-org/-/epics/14290

Proof of Concept (to see the whole picture): !159045 (closed)

In this MR we move GitlabSubscriptionHistory to GitlabSubscriptions::SubscriptionHistory so that the new entities are all under the same namespace

MR Cadence

MR	description
!159901 (merged)	👈 you're here
!159921 (merged)	Add relation between Namespace and GitlabSubscriptions::SubscriptionHistory
!159933 (closed)	Add subscription_history to Namespace GraphQL Type

MR acceptance checklist

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How to set up and validate locally

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