feat(sentry-logback): add encoder for message formatting

[norwood]

:scroll: Description

this adds support for logback encoders in the sentry appender

:bulb: Motivation and Context

this was previously added in https://github.com/getsentry/sentry-java/pull/794/files and was mentioned here https://github.com/getsentry/sentry-java/issues/2217

:green_heart: How did you test it?

added a test to the test suite tested against my own sentry instance that formatted messages go through

:pencil: Checklist

• [ ] I reviewed the submitted code
• [ ] I added tests to verify the changes
• [ ] I updated the docs if needed
• [ ] No breaking changes

:crystal_ball: Next steps