Add a way to disable providers in the configfile

Author: seveas

doc/content/documentation/host_discovery.md

@@ -58,6 +58,9 @@ As you can see, the name of a provider section foes not imply which provider is
 specify the. As a result of this, you can easily use multiple instances of the same provider type,
 and can wrap a provider in a cache provider without affecting other parts of the configuration.
 
+If you want to temporarily disable a provider in your configuration, you can add `enabled: false` to
+its parameters.
+
 # Host attributes
 
 Providers do not just return a list of host names. The power of Herd is that it can filter by any

registry.go

@@ -133,6 +133,10 @@ func (r *Registry) LoadProviders(c *viper.Viper) error {
 	for key := range c.AllSettings() {
 		ps := c.Sub(key)
 		pname := ps.GetString("Provider")
+		if ps.IsSet("Enabled") && !ps.GetBool("Enabled") {
+			logrus.Debugf("Skipping disabled provider %s", key)
+			continue
+		}
 		p, err := NewProvider(pname, key)
 		if err != nil {
 			rerr.Add(fmt.Errorf("Error parsing config for %s: %s", key, err))