Mattermost-server: [Help Wanted] Add unit tests to APIv4 for creating users with hashes and invite ids

[jasonblais]

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Notes: Jira ticket

In api4/user_test.go need to add tests for creating users with hashes and with invite ids. See the api/user_test.go for examples of how it was done in v3.

Might need to add more model/client4.go functions as well.

If you have questions or need help, ask in the APIv4 channel on the community Mattermost instance: https://pre-release.mattermost.com/core/channels/apiv4

[cpanato]

i will take this one

[cpanato]

PR: https://github.com/mattermost/platform/pull/6363