ci: assign version using release-please (#654)

This PR changes version number output to the following:

### Release
```
$ hcloud version
hcloud 1.23.4
```

### goreleaser --snapshot
```
$ hcloud version
hcloud 1.23.4-dev+<short commit id>
```

### go build/go install
```
$ hcloud version
hcloud 1.23.4-dev
```

Closes #636

---------

Co-authored-by: jo <ljonas@riseup.net>

.github/release-please-config.json

@@ -6,7 +6,8 @@
   "packages": {
     ".": {
       "release-type": "go",
-      "package-name": "hcloud-cli"
+      "package-name": "hcloud-cli",
+      "extra-files": ["internal/version/version.go"]
     }
   }
 }

.goreleaser.yml

@@ -7,7 +7,9 @@ builds:
     main: ./cmd/hcloud/main.go
     binary: hcloud
     ldflags:
-      - -w -X github.com/hetznercloud/cli/internal/version.Version={{.Version}}
+      - -w
+      - -X {{ .ModulePath }}/internal/version.version={{ .Version }}
+      - -X {{ .ModulePath }}/internal/version.versionPrerelease={{- if .IsSnapshot -}}dev+{{ .ShortCommit }}{{- end -}}
     env:
       - CGO_ENABLED=0
     goos:
@@ -27,7 +29,9 @@ builds:
     main: ./cmd/hcloud/main.go
     binary: hcloud
     ldflags:
-      - -w -X github.com/hetznercloud/cli/internal/version.Version={{.Version}}
+      - -w
+      - -X {{ .ModulePath }}/internal/version.version={{ .Version }}
+      - -X {{ .ModulePath }}/internal/version.versionPrerelease={{- if .IsSnapshot -}}dev+{{ .ShortCommit }}{{- end -}}
     env:
       - CGO_ENABLED=0
     goos:
@@ -40,6 +44,9 @@ builds:
         - cmd: bash script/gon.sh "{{ .Path }}"
           output: true
 
+snapshot:
+  name_template: "{{ .Version }}-dev+{{ .ShortCommit }}"
+
 checksum:
   name_template: checksums.txt
   algorithm: sha256

internal/version/version.go

@@ -1,4 +1,19 @@
 package version
 
-// Version is set via compiler flags (see goreleaser config)
-var Version = "unknown"
+var (
+	// version is a semver version (https://semver.org).
+	version = "1.41.1" // x-release-please-version
+
+	// versionPrerelease is a semver version pre-release identifier (https://semver.org).
+	//
+	// For final releases, we set this to an empty string.
+	versionPrerelease = "dev"
+
+	// Version of the hcloud CLI.
+	Version = func() string {
+		if versionPrerelease != "" {
+			return version + "-" + versionPrerelease
+		}
+		return version
+	}()
+)