Do not allow/support NAB CR spec update once its created

[shubham-pampattiwar]

Once a NAB CR spec is created by the user, the NAB controller should avoid updating the NAB CR spec if the user tries to modify the NBA object's spec values.

[mateusoliveira43]

is not this duplication of #77

[shubham-pampattiwar]

Nope this is different: In this scenario the user is trying to update an already created NAB CR. (User Update)
In the issue you linked the NAB controller is trying to sync NAB CR spec with the Velero Backup CR spec. (Controller Sync update)
Both of them should be avoided.