Add originalUser and authenticatedUser as selectors available for resource group selection

[xkrogen]

Description

This PR adds the original user and authenticated user as selectors that can be used in resource group selection, allowing for more flexible selection of resource groups based on additional context about the user's identity.

Additional context and related issues

Currently, resource group selection can take into account the current session user, but doesn't have a way to select based on the original user or authenticated user. In some setups, in may be desirable for resource group selection to be based on these additional metadata, rather than only the current user.

For original user, one sample use case is when SET SESSION AUTHORIZATION is used to change the current user for purposes of gaining access to a different set of resources (for example, a table that is accessible by the impersonated user, but not the original user). In this case, it can be desirable to still perform resource group selection based on the original user. For example, let us say that access to widely used table t_foo is only granted to user u_foo. Many users will impersonate u_foo to get access to t_foo, and if resource group selection is performed on the impersonated user, they will all share the same resource group, potentially causing contention. It may be desirable to instead perform resource group selection based on the original user to avoid such contention.

For authenticated user, a sample use case may be to identify all queries originating from a certain platform or service. If that platform/service has the ability to impersonate other users for authorization purposes, it may still be desirable to execute all queries in a dedicated resource group.

Release notes

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## Resource Groups
* Add `originalUser` and `authenticatedUser` as resource group selectors. ({issue}`24662`)

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[xkrogen]

cc @findepi @piotrrzysko

[xkrogen]

Had trouble getting the Oracle Flyway DB migration tests to run on my local so it took a few tries on CI to get that to pass. But it should be ready for review now!