Add serverchan3 support for serverchan notification provider

[easychen]

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Description

Fixes #(issue)

UptimeKuma has a notification provider called ServerChan that released a new branch version. This PR adds compatibility for the new branch (by adjusting the API entry through the Sendkey recognition)

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 generates no new warnings
• My code needed automated testing. I have added them (this is optional task)

[CommanderStorm]

Given that below changes the URL, could you please link to the docs where this is recommended?
Seems a bit sus otherwise to change to a different second level domain..

[easychen]

Official Website: https://sc3.ft07.com
Official Announcement: Chinese
I add a txt under sct.ftqq.com: https://sct.ftqq.com/md/sc3.txt

The reason for changing sendkey to be included in the domain is due to the constant cyclic requests to the API interface by some third-party programs. By using DNS to direct subdomains to 127.0.0.1, we can alleviate the burden on the server.😅

[CommanderStorm]

Thanks for the adjustments to the notification provider! 🎉

Note

This PR is part of the v2.0 merge window => see #4500 for the bugs that need to be addressed before we can ship this release ^^

_{All changes in this PR are small and uncontroversial ⇒ merging with junior maintainer approval}