add goreleaser configuration for binaries and deb/rpm packages

- build static binaries for linux, darwin and freebsd
- create deb and rpm packages that register gosh in /etc/shells
- publish releases to Gitea
- add --version flag, set at build time via ldflags

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -1 +1,2 @@
 gosh
+dist/