MM-56819: Introduce --local mode in MMCTL to handle user preferences.

[kaoski]

Summary

This commit introduces support for --local mode in MMCTL for managing user preferences. The following changes have been added:

1. API endpoints for user preferences are registered with the local router.
2. Test cases have been added to ensure functionality for both System Admins and --local mode.

Note: As there is no authentication/authorization required in --local mode, @mattermod suggested omitting session checks from the API handlers. But we are already bypassing session checks for local mode requests as detailed here. Hence, I have retained the existing session checks in place.

Ticket Link

Github Issue: #26864
Jira Ticket: https://mattermost.atlassian.net/browse/MM-56819

Release Note

Added --local mode support in MMCTL to handle user preferences.

[mm-cloud-bot]

@kaoski: 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.

I understand the commands that are listed here

[mattermost-build]

Hello @kaoski,

Thanks for your pull request! A Core Committer will review your pull request soon. For code contributions, you can learn more about the review process here.

[mattermost-build]

This PR has been automatically labelled "stale" because it hasn't had recent activity.
A core team member will check in on the status of the PR to help with questions.
Thank you for your contribution!