Add signature generation

Signed-off-by: Lukas Bachschwell <lukas@lbsfilm.at>

.goreleaser.yml

@@ -22,6 +22,22 @@ changelog:
     exclude:
       - '^docs:'
       - '^test:'
+signs:
+  - id: selfupdatesign
+
+    # path to the signature command
+    #
+    # defaults to `gpg`
+    cmd: openssl
+
+    # command line templateable arguments for the command
+    #
+    # to sign with a specific key use
+    # args: ["-u", "<key id, fingerprint, email, ...>", "--output", "${signature}", "--detach-sign", "${artifact}"]
+    #
+    # defaults to `["--output", "${signature}", "--detach-sign", "${artifact}"]`
+    args: ["dgst", "-sha256", "-sign", "privkey.pem", "${artifact}.sig", "${artifact}"]
+    artifacts: all
 gitea_urls:
   api: https://git.lbsfilm.at/api/v1/
   download: https://git.lbsfilm.at