Restrict rest-server.service SystemCallFilter (disallow @resources and @privileged)

[eriksjolund]

What is the purpose of this change? What does it change?

Add more systemcalls that should not be allowed to the SystemCallFilter= in rest-server.service.

Was the change discussed in an issue or in the forum before?

Yes, in the forum

https://forum.restic.net/t/adjust-systemcallfilter-in-rest-server-service-add-resources-and-privileged/6454/4

Checklist

• [x] I have enabled maintainer edits for this PR
• [ ] I have added tests for all changes in this PR
• [ ] I have added documentation for the changes (in the manual)
• [ ] There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• [ ] I have run gofmt on the code in all commits
• [ ] All commit messages are formatted in the same style as the other commits in the repo
• [ ] I'm done, this Pull Request is ready for review

[MichaelEischer]

Closing as the PR caused a crash during my tests.