Add API endpoint for minimal user profile information

[relm]

This PR adds a new endpoint to retrieve minimal user profile information - API_GetUserProfile.php

We use the existing API_GetUserSummary.php endpoint to check if a user exists as well as other details like their untracked/tracked status and then pull additional profile information based on that. This results in some unnecessary DB queries as we only really need fields from the main user table. So I propose adding this as a lighter alternative.

One argument is accepted - u which represents the user's username

Example output:

{
	"User": "Root",
	"MemberSince": "2023-12-09 19:24:46",
	"RichPresenceMsg": null,
	"LastGameID": 0,
	"ContribCount": 0,
	"ContribYield": 0,
	"TotalPoints": 1000,
	"TotalSoftcorePoints": 0,
	"TotalTruePoints": 1010,
	"Permissions": 4,
	"Untracked": 0,
	"ID": 1000001,
	"UserWallActive": 1,
	"Motto": "I am root",
	"UserPic": "\/UserPic\/root.png"
}

[wescopeland]

Thanks for submitting a PR.

Please add tests for any new endpoint.

Also, let's not add new functionality to any Helpers file unless absolutely necessary. We plan on phasing these out soon. As an alternative, perhaps it would just be best for this new functionality to live within the endpoint itself.

[wescopeland]

#2090 may be a helpful reference.

[relm]

Done! Moved the functionality to the endpoint itself and added tests.

Tests added and code refactored

[wescopeland]

Looks great. A few minor nits.

[relm]

Should be good now!