fix: DPE-7356 mitigate instance blocking (#439)

## Issue

See issue #438

## Solution

Change defaults for quarantining instances to avoid upstream bug.

Fix #438

## Test

Available build in branch `8.0/edge/dns` | rev744 (_for amd64 only_):

```sh
juju deploy mysql-router-k8s --trust --channel 8.0/edge/dns
```

---------

Co-authored-by: Carl Csaposs <[email protected]>

Author: paulomach

spread.yaml

@@ -79,6 +79,8 @@ backends:
       PermitEmptyPasswords yes
       EOF
 
+      sudo passwd --delete "$USER"
+
       ADDRESS localhost
     # HACK: spread does not pass environment variables set on runner
     # Manually pass specific environment variables

src/workload.py

@@ -252,6 +252,13 @@ def _get_bootstrap_command(
             "--conf-set-option",
             f"http_auth_backend:default_auth_backend.filename={self._container.rest_api_credentials_file.relative_to_container}",
             "--conf-use-gr-notifications",
+            # destination_status added to workaround MySQL Router bug
+            # https://bugs.mysql.com/bug.php?id=118059
+            # TODO: Remove once fixed on upstream
+            "--conf-set-option",
+            "destination_status.error_quarantine_threshold=3",
+            "--conf-set-option",
+            "destination_status.error_quarantine_interval=5",
         ]
 
     def _bootstrap_router(self, *, event, tls: bool) -> None: