Support file upload

This allows an sftp client to upload data to the Permanent virtual
filesystem.  Unfortunately the way sftp works there is no way of knowing
how large a file is going to be until after the handle is closed, and
unfortunately permanent requires us to know how large the file is before
it will allow us to generate a presigned post.

This means our solution is to write the file into temporary storage.
This is a potential vulnerability and should be seen as a short term
solution.

Other limitations of this implementation include:

1. Lack of support for editing files
2. Lack of support for updating modtime

All of these will need to be improved in future developments.

Issue #48 Implement file open / write handlers

package.json

@@ -40,7 +40,8 @@
     "@babel/preset-typescript": "^7.16.7",
     "@tsconfig/node16": "^1.0.2",
     "@types/node-fetch": "^2.6.2",
-    "@types/ssh2": "^1.11.4",
+    "@types/ssh2": "^1.11.7",
+    "@types/tmp": "^0.2.3",
     "@types/uuid": "^8.3.4",
     "@typescript-eslint/eslint-plugin": "^5.9.0",
     "@typescript-eslint/parser": "^5.9.0",
@@ -60,6 +61,7 @@
     "logform": "^2.3.2",
     "node-fetch": "^2.6.7",
     "ssh2": "^1.11.0",
+    "tmp": "^0.2.1",
     "uuid": "^8.3.2",
     "winston": "^3.4.0"
   }