API: Add user online stats

[hossinasaadi]

implement custom counter for ips connected to each client by email

1. add statsUserOnline to config.json add statsUserOnline bool to policy

      "levels": {
        "0": {
          "statsUserDownlink": true,
          "statsUserUplink": true,
**        "statsUserOnline": true

        },  

2. each ip will remain in list for 20 sec (may we can add custom value to config) 0b8ad84
3. client should have an email.
4. get user online from api :

./xray api statsonline -server=127.0.0.1:8080 -email "user1@test.com"
{
   "stat":  {
       "name":  "user>>>user1@test.com>>>online",
       "value":  "3"
   }
}

this implementation based on #2277 (comment) discussion and may needs some review to improve and suggestions.
@mmmray @yuhan6665

[mmmray]

hello @amir-devman please review if this API is sufficient for your usecase as well. the implementation looks fine to me at a glance, as it is disabled by default performance doesn't seem critical.

[APT-ZERO]

each ip will remain in list for 20 sec (may we can add custom value to config)

That is a good option
You can also add option to NOT mark a user as Online, if it's not connected for more than N seconds (if user just did a Real-Delay test, it's not online)

[yuhan6665]

Looks good to me! Thanks for the effort to move to API solution. I will close #2277 for now

[hossinasaadi]

each ip will remain in list for 20 sec (may we can add custom value to config)

That is a good option You can also add option to NOT mark a user as Online, if it's not connected for more than N seconds (if user just did a Real-Delay test, it's not online)

that's a good idea, checking what i can do.

[RPRX]

#3644 (comment)

[willstore69]

Cannot Checking Number User Online Stats While Using Xray Fallback Xtls Vision 443

===
When using the Xray API to check online user stats, the command xray api statsonline -server=127.0.0.1:10087 -email "segs" is returning the following output:

{
"stat": {
"name": "user>>>segs>>>online"
}
}

The output indicates that the user is online but does not show the expected value for the number ip login.