Bitbucket becomes unusable when the user exits from the Maintenance mode when there is a running backup task.

Steps to reproduce

1. Enter the Maintenance mode:

   λ: curl -L -s -f -u "admin" -X POST -H "Content-type: application/json" "http://localhost:7990/mvc/maintenance/lock" | jq .
   Enter host password for user 'admin':
   {
     "unlockToken": "db666f4896521fae93c7947c089d1d468f26c55f",
     "owner": {
       "displayName": "admin",
       "name": "admin"
     }
   }
   

   λ: curl -L -s -f http://localhost:7990/status | jq .
   {
     "state": "MAINTENANCE"
   }
   

2. Before starting the backup task:

   λ: curl -L -s -f -u "admin" -X GET -H "X-Atlassian-Maintenance-Token: db666f4896521fae93c7947c089d1d468f26c55f" -H "Accept: application/json" -H "Content-type: application/json" "http://localhost:7990/mvc/maintenance" | jq .
   Enter host password for user 'admin':
   {
     "task": null,
     "db-state": "AVAILABLE",
     "scm-state": "AVAILABLE"
   }
   

3. Start backup task:

   λ: curl -L -s -f -u "admin" -X POST -H "X-Atlassian-Maintenance-Token: db666f4896521fae93c7947c089d1d468f26c55f" -H "Accept: application/json" -H "Content-type: application/json" "http://localhost:7990/mvc/admin/backups?external=true" | jq .
   Enter host password for user 'admin':
   {
     "id": "6210e1ad-f898-42e4-b332-ba292fde8213",
     "progress": {
       "message": "Closing database connections",
       "percentage": 0
     },
     "state": "RUNNING",
     "type": "BACKUP",
     "cancelToken": "365c5ab8fba24d59276276f4aeb90395468a456c"
   }
   

4. After starting the backup task:

   λ: curl -L -s -f -u "admin" -X GET -H "X-Atlassian-Maintenance-Token: db666f4896521fae93c7947c089d1d468f26c55f" -H "Accept: application/json" -H "Content-type: application/json" "http://localhost:7990/mvc/maintenance" | jq .
   Enter host password for user 'admin':
   {
     "task": {
       "id": "6210e1ad-f898-42e4-b332-ba292fde8213",
       "progress": {
         "message": "Backing up Bitbucket home",
         "percentage": 10
       },
       "state": "RUNNING",
       "type": "BACKUP"
     },
     "db-state": "DRAINED",
     "scm-state": "DRAINED"
   }
   

   The backup percentage will automatically be set to 10%.

Current behaviour:

The system allows users to exit the Maintenance mode:

λ: curl -L -s -f -u "admin" -X DELETE -H "Accept: application/json" -H "Content-type: application/json" "http://localhost:7990/mvc/maintenance/lock?token=db666f4896521fae93c7947c089d1d468f26c55f"
Enter host password for user 'admin':

The following log messages will be logged into atlassian-bitbucket.log:

2024-09-04 05:42:36,409 INFO  [hz.hazelcast.cached.thread-10]  c.a.s.i.m.DefaultMaintenanceLock Maintenance has been completed. The system lock has been released

The Bitbucket state and the backup task will remain unchanged:

λ: curl -L -s -f http://localhost:7990/status | jq .
{
  "state": "MAINTENANCE"
}

λ: curl -L -s -f http://localhost:7990/status | jq .
λ: curl -L -s -f -u "admin" -X GET -H "X-Atlassian-Maintenance-Token: db666f4896521fae93c7947c089d1d468f26c55f" -H "Accept: application/json" -H "Content-type: application/json" "http://localhost:7990/mvc/maintenance" | jq .
Enter host password for user 'admin':
{
  "task": {
    "id": "6210e1ad-f898-42e4-b332-ba292fde8213",
    "progress": {
      "message": "Backing up Bitbucket home",
      "percentage": 10
    },
    "state": "RUNNING",
    "type": "BACKUP"
  },
  "db-state": "DRAINED",
  "scm-state": "DRAINED"
}

Bitbucket will remain in an unusable state until the user restarts Bitbucket.

Expected behaviour:

When there is a running backup task, the system should not allow users to exit the Maintenance mode.

The system should throw an error message saying that a backup task is running. To exit Maintenance mode, the user should cancel the backup task or update the backup progress to 100.

curl -L -s -f -u "<<admin username>>" -X POST -H "Accept: application/json" -H "Content-type: application/json" "<<base url>>/mvc/admin/backups/progress/client?token=<<lock_token>>&percentage=100"