[Security] rpm package is unsigned

**Problem:**

Peergos' `rpm` package is not signed, which can lead to problems depending on the security policy of `dnf` and gets blocked if `localpkg_gpgcheck = 1`. It can also lead to problems on systems with signature-based application control.

```
$ rpm -qi peergos-1.18.0-linux-amd64.rpm | grep Signature
Signature   : (none)
```

**Proposed solution:** 

Sign package