cmd, internal/build, docker: advertise commit date in unstable build versions (#19522)

* add-date-to unstable

* fields-insteadof-split

* internal/build: support building with missing git

* docker: add git history back to support commit date in version

* internal/build: use PR commits hashes for PR builds

cmd/swarm/global-store/main.go

@@ -26,6 +26,7 @@ import (
 var (
 	version   = "0.1"
 	gitCommit string // Git SHA1 commit hash of the release (set via linker flags)
+	gitDate   string
 )
 
 func main() {
@@ -45,6 +46,9 @@ func newApp() (app *cli.App) {
 	if len(gitCommit) >= 8 {
 		app.Version += "-" + gitCommit[:8]
 	}
+	if gitDate != "" {
+		app.Version += "-" + gitDate
+	}
 	app.Usage = "Swarm Global Store"
 
 	// app flags (for all commands)