Give an option to block plan updates when metadata settings differs

[rogalv]

With 2.1.0, a metadata search configs could be added to services and plans. On a plan update, if metadata settings differs from initial value, metadata search is disabled on a bucket.
Please, add an option to decide what to do on plan change when metadata search settings are different from what is applied on instance:

• throw an error
• disable metadata
• ignore changes and leave metadata as is.