[Zone Decommission] Fail weight update when decommission ongoing and fail decommission when attribute not weighed away

[imRishN]

Is your feature request related to a problem? Please describe.
While triggering weight update for an awareness attribute, we should check if any ongoing decommission action is in process. If yes, we should fail the weight update request as it might lead cluster to an unexpected state where weights would be set to a decommissioned zone or for that matter any such state update. During decommission we are already stopping any traffic in one attribute. Any weight update during this can have cascading effect.

Also, before executing decommission we should check if the to-be-decommissioned attribute is already weighed away. If not, we should fail the decommission action.

[imRishN]

PR merged