Updated formula regexp to support ?ref= syntax.

Added formulas docs for salt-masterless provisioner

Signed-off-by: Andrew Cornies <acornies@gmail.com>

provisioner/salt-masterless/provisioner.go

@@ -448,7 +448,7 @@ func validateFileConfig(path string, name string, required bool) error {
 }
 
 func hasValidFormulaURLs(s []string) bool {
-	re := regexp.MustCompile(`^(.*).git\/\/[a-zA-Z0-9-_]+$`)
+	re := regexp.MustCompile(`^(.*).git\/\/[a-zA-Z0-9-_]+(\?.*)?$`)
 
 	for _, u := range s {
 		if !re.MatchString(u) {

provisioner/salt-masterless/provisioner_test.go

@@ -348,6 +348,7 @@ func TestProvisionerPrepare_ValidFormulaURLs(t *testing.T) {
 	config["formulas"] = []string{
 		"git::https://github.com/org/some-formula.git//example",
 		"git@github.com:org/some-formula.git//example",
+		"git::https://github.com/org/some-formula.git//example?ref=example",
 	}
 
 	err := p.Prepare(config)

website/pages/docs/provisioners/salt-masterless.mdx

@@ -100,4 +100,9 @@ Optional:
 - `guest_os_type` (string) - The target guest OS type, either "unix" or
   "windows".
 
+- `formulas` (array of strings) - An array of git source formulas to be downloaded to the local
+  state tree prior to moving to the remote state tree. Note: `//directory` must be included in 
+  the URL to download the appropriate formula directory. Example:
+  `git::https://github.com/saltstack-formulas/vault-formula.git//vault?ref=v1.2.3`
+
 @include 'provisioners/common-config.mdx'