update docs for `manage-users` and user API provider

Enhancement Type

Improve an existing feature

Describe the enhancement

Documentation Link: Server Properties - OPs/Administrators

Problem
When using the manage-users command to add an OP/whitelisted player with an Xbox/Microsoft Account (MSA), the container fails to start with the error:

[mc-image-helper] ERROR: Invalid parameter provided for 'manage-users' command: Could not resolve user from Playerdb

The Mojang API (https://api.mojang.com/users/profiles/minecraft/:username) returns:

{"errorMessage": "Couldn't find any profile with name :username"}

Even though the profile exists on:

• Xbox Profile
• Minecraft.net Profile

Root Cause
Different Java Profile Name and xbox gametag.

Solution Use username from Java Profile Name. Or change it there to gametag value.