Add expand call metadata property

[mahaker]

Summary

When this property is enabled, include the user-level access token.
Docs is here.

Ticket Link

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Related Pull Requests

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• Has server changes (please link here)
• Has mobile changes (please link here)

Screenshots

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Release Note

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[mm-cloud-bot]

@mahaker: Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[mattermost-build]

E2E tests not automatically triggered, because PR has no approval yet. Please ask a developer to review and then try again to attach the QA label.

[M-ZubairAhmed]

@mahaker please open the PR in https://github.com/mattermost/mattermost-server its where the monorepo lives now.