feat: catalogue generate now rate limits

Closes coop-cloud/organising#231.

cli/catalogue/generate.go

@@ -11,6 +11,7 @@ import (
 	"coopcloud.tech/abra/pkg/catalogue"
 	"coopcloud.tech/abra/pkg/config"
 	"coopcloud.tech/abra/pkg/git"
+	"coopcloud.tech/abra/pkg/limit"
 	"github.com/sirupsen/logrus"
 	"github.com/urfave/cli/v2"
 )
@@ -74,10 +75,14 @@ var catalogueGenerateCommand = &cli.Command{
 
 		logrus.Debugf("ensuring '%v' recipe(s) are locally present and up-to-date", len(repos))
 
+		cloneLimiter := limit.New(10)
 		retrieveBar := formatter.CreateProgressbar(len(repos), "retrieving recipes...")
 		ch := make(chan string, len(repos))
 		for _, repoMeta := range repos {
 			go func(rm catalogue.RepoMeta) {
+				cloneLimiter.Begin()
+				defer cloneLimiter.End()
+
 				if recipeName != "" && recipeName != rm.Name {
 					ch <- rm.Name
 					retrieveBar.Add(1)

pkg/limit/limit.go

@@ -0,0 +1,20 @@
+package limit // https://github.com/tidwall/limiter
+
+// Limiter is for limiting the number of concurrent operations. This
+type Limiter struct{ sem chan struct{} }
+
+// New returns a new Limiter. The limit param is the maximum number of
+// concurrent operations.
+func New(limit int) *Limiter {
+	return &Limiter{make(chan struct{}, limit)}
+}
+
+// Begin an operation.
+func (l *Limiter) Begin() {
+	l.sem <- struct{}{}
+}
+
+// End the operation.
+func (l *Limiter) End() {
+	<-l.sem
+}