Only allow a single migration to happen at a time for Chef Server

[kalroy]

User Story

As an Automate User, I should be able to run only one migration at a time.

Acceptance Criteria

• In case if there is a running migration, we should return error

Implementation Details

• In the fetch organisation API, first check the status of the latest run.
• In case there is an In Progress migration, return an error

Definition of Done

• All things specified in User Story Acceptance Criteria should be fulfilled.
• All Exceptions are Handled Properly
• Ensure logs have no unnecessary data.
• Test coverage for the new feature is done to at least 70%
• If needed raise Docs PR and tag documentation.
• Swagger Documentation updated
• Smoke Test done.
• Ensure Build and Integration Pipelines are Green.
• PR has 2 approvers.
• All Code Review Comments are Resolved.
• README doc should be updated, if needed.