feat: Allow digits as slug's first character (#4647)

  We used to forbid digits as an instance slug's first character
  probably because of limitations in CouchDB.

  Now that we use prefixes for our databases names we probably don't
  need this check which is pretty limitating when it comes to using data
  from third-party SSOs for example.

Author: taratatach

model/instance/lifecycle/helpers.go

@@ -161,7 +161,7 @@ func checkAliases(inst *instance.Instance, aliases []string) ([]string, error) {
 }
 
 const illegalChars = " /,;&?#@|='\"\t\r\n\x00"
-const illegalFirstChars = "0123456789."
+const illegalFirstChars = "."
 
 func validateDomain(domain string) (string, error) {
 	var err error

model/instance/lifecycle/lifecycle_test.go

@@ -88,6 +88,12 @@ func TestLifecycle(t *testing.T) {
 			assert.NotEmpty(t, instance.ID())
 			assert.Equal(t, instance.Domain, "test.cozycloud.cc")
 		}
+
+		_, err = lifecycle.Create(&lifecycle.Options{
+			Domain: "1test.cozycloud.cc",
+			Locale: "en",
+		})
+		assert.NoError(t, err)
 	})
 
 	t.Run("CreateInstanceWithFewSettings", func(t *testing.T) {
@@ -169,6 +175,12 @@ func TestLifecycle(t *testing.T) {
 			Locale: "en",
 		})
 		assert.Error(t, err, "An error is expected")
+
+		_, err = lifecycle.Create(&lifecycle.Options{
+			Domain: ".foo.cozycloud.cc",
+			Locale: "en",
+		})
+		assert.Error(t, err, "An error is expected")
 	})
 
 	t.Run("GetWrongInstance", func(t *testing.T) {