Add Serilog.xml in formatsDirectory

[andriibratanin]

A trivial example of log highlighting format for Serilog that matches the default File Sink log message template, like:

2024-08-17 02:46:37.175 +03:00 [WRN] Running in Development environment
2024-08-17 02:46:37.206 +03:00 [INF] MainBackgroundService has started
2024-08-17 02:48:18.774 +03:00 [INF] MainBackgroundService has exited
2024-08-17 02:48:18.775 +03:00 [ERR] Exit code is non-zero!

Note: Manual steps required until the following issue is fixed: #191
Until then, after log format import users have to manually add three additional highlighting patterns:

• "^\serr\s$" - for errors
• "^\swrn\s$" - for warnings
• "^\sinf\s$" - for information messages

Partially resolves:
#43