Fix handling of IPv6 addresses in getClientIP

[n-thumann]

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Description

This PR fixes the handling of IPv6 addresses in getClientIP. Currently this method fails to handle IPv6 addresses correctly. E.g. my log shows:

2023-07-08T00:15:01+02:00 [RATE-LIMIT] INFO: remaining requests: 19
2023-07-08T00:15:01+02:00 [AUTH] INFO: Successfully logged in user admin. IP=ca44
2023-07-08T00:15:02+02:00 [SETTINGS] DEBUG: Get Setting: initServerTimezone: null

when I logged in from xxxx:xxxx:xxxx:xxxx:59a9:4a64:bea4:ca44.

This is fixed by not blindly removing anything prefix the :, but only the relevant part (I suspect that this as been introduced in the first place to remove the prefix of IPv4-mapped IPv6 addresses):

> clientIP = "2001:db8::1"
'2001:db8::1'
> clientIP.replace(/^.*:/, "")
'1'
> clientIP.replace(/^::ffff:/, "")
'2001:db8::1'

> clientIP = "::ffff:127.0.0.1"
'::ffff:127.0.0.1'
> clientIP.replace(/^.*:/, "")
'127.0.0.1'
> clientIP.replace(/^::ffff:/, "")
'127.0.0.1'

The log now contains:

2023-07-08T00:16:02+02:00 [RATE-LIMIT] INFO: remaining requests: 19
2023-07-08T00:16:02+02:00 [AUTH] INFO: Successfully logged in user admin. IP=xxxx:xxxx:xxxx:xxxx:59a9:4a64:bea4:ca44
2023-07-08T00:16:02+02:00 [SETTINGS] DEBUG: Get Setting (cache): initServerTimezone: true

Type of change

Please delete any options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas
  (including JSDoc for methods)
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)

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[chakflying]

getClientIP has unit tests defined in test/backend.spec.js. Maybe you can add appropriate test cases there.

[n-thumann]

getClientIP has unit tests defined in test/backend.spec.js. Maybe you can add appropriate test cases there.

Done :)