Allow configuration of substring search for searching sharees

This introduces new settings for the users and groups services.
"group_substring_filter_type" for the group services and
"user_substring_filter_type" for the users service. They allow to set
the type of LDAP filter that is used for substring user searches.
Possible values are: "initial", "final" and "any" to do either prefix,
suffix or full substring searches.

Fixes #547

services/users/pkg/config/defaults/defaultconfig.go

@@ -36,19 +36,20 @@ func DefaultConfig() *config.Config {
 		Driver: "ldap",
 		Drivers: config.Drivers{
 			LDAP: config.LDAPDriver{
-				URI:              "ldaps://localhost:9235",
-				CACert:           filepath.Join(defaults.BaseDataPath(), "idm", "ldap.crt"),
-				Insecure:         false,
-				UserBaseDN:       "ou=users,o=libregraph-idm",
-				GroupBaseDN:      "ou=groups,o=libregraph-idm",
-				UserScope:        "sub",
-				GroupScope:       "sub",
-				UserFilter:       "",
-				GroupFilter:      "",
-				UserObjectClass:  "inetOrgPerson",
-				GroupObjectClass: "groupOfNames",
-				BindDN:           "uid=reva,ou=sysusers,o=libregraph-idm",
-				IDP:              "https://localhost:9200",
+				URI:                     "ldaps://localhost:9235",
+				CACert:                  filepath.Join(defaults.BaseDataPath(), "idm", "ldap.crt"),
+				Insecure:                false,
+				UserBaseDN:              "ou=users,o=libregraph-idm",
+				GroupBaseDN:             "ou=groups,o=libregraph-idm",
+				UserScope:               "sub",
+				GroupScope:              "sub",
+				UserSubstringFilterType: "initial",
+				UserFilter:              "",
+				GroupFilter:             "",
+				UserObjectClass:         "inetOrgPerson",
+				GroupObjectClass:        "groupOfNames",
+				BindDN:                  "uid=reva,ou=sysusers,o=libregraph-idm",
+				IDP:                     "https://localhost:9200",
 				UserSchema: config.LDAPUserSchema{
 					ID:          "ownclouduuid",
 					Mail:        "mail",