Add version to /status endpoint

[nitrocode]

what

• Add version to /status endpoint

why

• Much easier to identify what version is actively running

references

• Finally closes Return atlantis version when hitting /status #1119
• Previous PR Add Version to /healthz endpoint #1120
• and helpful comments from @lkysow !

commands

CGO_ENABLED=0 GOOS=darwin GOARCH=amd64 go build -v -o atlantis .
./atlantis server --gh-user=nitrocode --repo-allowlist=atlantis

✗ curl localhost:4141/status
{
  "shutting_down": false,
  "in_progress_operations": 0,
  "version": "0.19.3"
}