Add support for storing more complex validations in definitions

[shirshendu]

Currently in

commons/tendrl/commons/objects/definition/master.yaml

Line 268 in 43d544d

volume_profiling_flag:

:
an attribute would have a help and a type.

        volume_profiling_flag:
          help: Whether to enable/disable/leave as-is volume profiling
          type: String

Let us start adding support for more complex validations, possibly under a validations key.
For example, in the above example, we should have the volume_profiling_flag attribute as a String, as well as one-of-n values.

How about something like this:

        volume_profiling_flag:
          help: Whether to enable/disable/leave as-is volume profiling
          type: String
          validations:
            type: String
            inclusion:
              - enable
              - disable
              - 'leave-as-is'            

It is up for discussion if we want to repeat the type: String in the validation as well. I would suggest being explicit, because we may have an attribute that needs to be casted if present, but not validated.