Mattermost-server: UI Automation: Write an automated test using Cypress for "Can change Support Email setting"

[saturninoabril]

Test Key: SC20337

Test file: /cypress/integration/system_console/ui_and_api/customization_spec.js

Title: Can change Support Email setting

Steps:

1. Login as sysadmin and visit the page "/admin_console/site_config/customization" directly
2. Change set value and save

Expected:

1. Verify that the setting, help text and set value is visible and match text
2. Verify that the value is save, directly via REST API

See our end-to-end testing documentation for reference.

Jira ticket: MM-20337

Sample PR: https://github.com/mattermost/mattermost-webapp/pull/4262/files

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[themaverikk]

I'd like to work on this.