chore: Change getDeviceTime to call the mobile implementation

[mykola-mokhnach]

Types of changes

• No changes in production code.
• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Details

Selenium webdriver implementation ignores parameters passed into GET requests. This PR replaces the call with parameters with the corresponding mobile: endpoint implementation to make it working properly. See appium/appium#14141

[markbearden]

Informational note: The main Appium documentation for the system_time endpoint, and the Appium-hosted copy of the Java client's getDeviceTime(), do not yet indicate any support for the "format" parameter that this change is adding. (I am wondering from where came the expectation that the client could ask the Appium server to format the time response, when that appears to have never been supported/documented for the Appium server? The source of this request, other than the issue reporter's assumption, is not explicitly indicated either here or at appium/appium#14141; that is, what specification was being complied with by making this change to the Java Appium client?)