add support for build tag to allow to disable some features

The following build tags are available:

- "nogcs", disable Google Cloud Storage backend
- "nos3", disable S3 Compabible Object Storage backends
- "nobolt", disable Bolt data provider
- "nomysql", disable MySQL data provider
- "nopgsql", disable PostgreSQL data provider
- "nosqlite", disable SQLite data provider
- "noportable", disable portable mode

httpd/schema/openapi.yaml

@@ -2,7 +2,7 @@ openapi: 3.0.1
 info:
   title: SFTPGo
   description: 'SFTPGo REST API'
-  version: 1.8.5
+  version: 1.8.6
 
 servers:
 - url: /api/v1
@@ -1278,6 +1278,11 @@ components:
           type: string
         commit_hash:
           type: string
+        features:
+          type: array
+          items:
+            type: string
+          description: Features for the current build. Available features are "portable", "bolt", "mysql", "sqlite", "pgsql", "s3", "gcs". If a feature is available it has a "+" prefix, otherwise a "-" prefix
   securitySchemes:
     BasicAuth:
       type: http