Validate upload size against the node limit before uploading

Expose the node's upload_size on the client server resource and reject
files over it in the file manager before any bytes are sent.

tests/Fixtures/api/client/servers.as-admin.json

@@ -14,6 +14,7 @@
                 "name": "Survival",
                 "node": "node-alpha",
                 "is_node_under_maintenance": false,
+                "upload_size": 100,
                 "sftp_details": {
                     "ip": "alpha.example.test",
                     "port": 2022
@@ -420,6 +421,7 @@
                 "name": "Admin Lab",
                 "node": "node-beta",
                 "is_node_under_maintenance": false,
+                "upload_size": 256,
                 "sftp_details": {
                     "ip": "beta.example.test",
                     "port": 2222