Merge pull request #1044 from Aflynn50/fix-microk8s-proxy-issue

#1044

The temporary file used to store the ca_cert was set to delete itself on close. This meant that when it was accessed multiple times it would no longer be present.

Set to not delete on close and to remove file when the proxy is deleted.

#### QA Steps
```
juju bootstrap microk8s
juju add-model default
juju deploy cos-lite
```
In python
```
from juju import model
m = model.Model()
await m.connect()
await m.create_offer("grafana:grafana-dashboard", "grafana-dashboards")
await m.disconnect()
```
Check all resource in /tmp have been cleaned up


Fixes #1040

juju/client/proxy/kubernetes/proxy.py

@@ -1,12 +1,15 @@
 # Copyright 2023 Canonical Ltd.
 # Licensed under the Apache V2, see LICENCE file for details.
-
+import os
 import tempfile
+import logging
 
 from juju.client.proxy.proxy import Proxy, ProxyNotConnectedError
 from kubernetes import client
 from kubernetes.stream import portforward
 
+log = logging.getLogger('juju.client.connection')
+
 
 class KubernetesProxy(Proxy):
     def __init__(
@@ -33,7 +36,7 @@ def __init__(
             raise ValueError("Invalid port number: {}".format(remote_port))
 
         if ca_cert:
-            self.temp_ca_file = tempfile.NamedTemporaryFile()
+            self.temp_ca_file = tempfile.NamedTemporaryFile(delete=False)
             self.temp_ca_file.write(bytes(ca_cert, 'utf-8'))
             self.temp_ca_file.flush()
             config.ssl_ca_cert = self.temp_ca_file.name
@@ -60,6 +63,10 @@ def connect(self):
 
     def __del__(self):
         self.close()
+        try:
+            os.unlink(self.temp_ca_file.name)
+        except FileNotFoundError:
+            log.debug(f"file {self.temp_ca_file.name} not found")
 
     def close(self):
         try: