[FEATURE] Add validation to request params during `/execute` methods

[pyek-bot]

Is your feature request related to a problem?
Validate the input params before they are parsed when using the /execute method.

What solution would you like?
A single execute API is used for executing different types of tasks (FunctionName). There is an MLInput class which is used to store the parsed input to this APIs. We should extend the validate method to validate different fields based on the FunctionName that is being executed and call this validate method before parsing the input.

[dhrubo-os]

Thanks for creating this issue? Can I assign this to you?

[pyek-bot]

Sure, thanks!