Add configuration option for settings Borg's temporary directory (#341).

Reviewed-on: https://projects.torsion.org/witten/borgmatic/pulls/356

borgmatic/borg/environment.py

@@ -9,6 +9,7 @@ OPTION_TO_ENVIRONMENT_VARIABLE = {
     'encryption_passcommand': 'BORG_PASSCOMMAND',
     'encryption_passphrase': 'BORG_PASSPHRASE',
     'ssh_command': 'BORG_RSH',
+    'temporary_directory': 'TMPDIR',
 }
 
 DEFAULT_BOOL_OPTION_TO_ENVIRONMENT_VARIABLE = {

borgmatic/config/schema.yaml

@@ -228,6 +228,12 @@ map:
                     Remote network upload rate limit in kiBytes/second. Defaults
                     to unlimited.
                 example: 100
+            temporary_directory:
+                type: str
+                desc: |
+                    Directory where temporary files are stored. Defaults to
+                    $TMPDIR
+                example: /path/to/tmpdir
             ssh_command:
                 type: str
                 desc: |