examples: add a script for bulk user update

you can use this sample script a a basis if you need to update
some common parameters for multiple users while preserving the others

examples/bulkupdate/README.md

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+# Bulk user update
+
+The `bulkuserupdate` example script shows how to use the SFTPGo REST API to easily update some common parameters for multiple users while preserving the others.
+
+The script is written in Python and has the following requirements:
+
+- python3 or python2
+- python [Requests](https://requests.readthedocs.io/en/master/) module
+
+The provided example tries to connect to an SFTPGo instance running on `127.0.0.1:8080` using the following credentials:
+
+- username: `admin`
+- password: `password`
+
+and it updates some fields for `user1`, `user2` and `user3`.
+
+Please edit the script according to your needs.

examples/bulkupdate/bulkuserupdate

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+#!/usr/bin/env python
+
+import posixpath
+import sys
+
+import requests
+
+try:
+	import urllib.parse as urlparse
+except ImportError:
+	import urlparse
+
+# change base_url to point to your SFTPGo installation
+base_url = "http://127.0.0.1:8080"
+# set to False if you want to skip TLS certificate validation
+verify_tls_cert = True
+# set the credentials for a valid admin here
+admin_user = "admin"
+admin_password = "password"
+# insert here the users you want to update
+users_to_update = ["user1", "user2", "user3"]
+# set here the fields you need to update
+fields_to_update = {"status":0, "quota_files": 1000, "additional_info":"updated using the bulkuserupdate example script"}
+
+# get a JWT token
+auth = requests.auth.HTTPBasicAuth(admin_user, admin_password)
+r = requests.get(urlparse.urljoin(base_url, "api/v2/token"), auth=auth, verify=verify_tls_cert)
+if r.status_code != 200:
+	print("error getting access token: {}".format(r.text))
+	sys.exit(1)
+access_token = r.json()["access_token"]
+auth_header = {"Authorization": "Bearer " + access_token}
+
+for username in users_to_update:
+	r = requests.get(urlparse.urljoin(base_url, posixpath.join("api/v2/users", username)),
+					headers=auth_header, verify=verify_tls_cert)
+	if r.status_code != 200:
+		print("error getting user {}: {}".format(username, r.text))
+		continue
+	user = r.json()
+	user.update(fields_to_update)
+	r = requests.put(urlparse.urljoin(base_url, posixpath.join("api/v2/users", username)),
+					headers=auth_header, verify=verify_tls_cert, json=user)
+	if r.status_code == 200:
+		print("user {} updated".format(username))
+	else:
+		print("error updating user {}, response code: {} response text: {}".format(username,
+																				r.status_code,
+																				r.text))