identity: Resolve conflicts with rename

[mpalmi]

Description

This PR introduces a new type of conflict resolution for duplicate Entities and Groups. This provides a way of preventing Vault from entering case-sensitive mode, which is the current behavior for any kind of duplicate.

Renames append the conflicting identity artifact's UUID to its name and updates a metadata field to indicate the pre-existing artifact's UUID.

The feature is gated by the force-identity-deduplication activation flag.

In order to maintain consistent behavior between the reporting resolver and the rename operation, we need to adjust the behavior of generated reports. Previously, they intentionally preserved existing Group merge determinism, wherein the last MemDB update would win and all others would be renamed. This approach is more complicated for the rename resolver, since we would need to update any duplicated entity in the cache while inserting the new duplicate (resulting in two MemDB operations). Though we can ensure atomic updates of the two identity artifacts with transactions (which we could get for groups with a minor adjustment, and we will get along with the Entity load speedups PR), it's far simpler to just rename all but the first insert as proposed in the current PR.

Since the feature is gated by an activation flag, with appropriate warnings of potential changes via the reporting resolver, I've opted for simplicity over maintaining pre-existing behavior. We can revisit this assumption later if we think alignment with existing behavior outweighs any potential complexity in the rename operation.

Entity alias resolution is left alone as a destructive merge operation to prevent a potentially high-impact change in existing behavior.

ENT PR: https://github.com/hashicorp/vault-enterprise/pull/7239
Resolves: VAULT-33094

TODO only if you're a HashiCorp employee

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  of a public function, even if that change is in a CE file, double check that
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  break any tests. Sometimes ENT only tests rely on public functions in CE
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