Add SerwerSMS.pl notification provider

[kffl]

Description

This PR adds support for SerwerSMS.pl as a notification provider via the HTTPS API v2: https://dev.serwersms.pl/https-api-v2/wysylanie-wiadomosci-sms-o-jednakowej-tresci

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

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 test it
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)