[Core feature] Support for Optional value types in Tasks

[kumare3]

Motivation: Why do you think this is important?

Recently UnionTypes were added to Flyte by the Latch team.
Though they are really powerful, it does introduce some complexity in how the type system handles it.
One of the powerful features is that it can support optional types easily. Optional types are of the form Optional<int>.
Optional types are great as they help in interface evolution.

Define: Interface evolution
Assume we have one task with the following interface

def task1(x: int, y: str) -> int

Now if a workflow references this task, but at some point the original maintainer of the task wants to update the task without affecting the other users of the task. Today Flyte supports this using version pinning. But, what if we want to update the versions?
This can be handled in one of two ways, either by supporting Optional types and or default values. Optional types is a simplification of default values with only None as the supported default.
Thus it would be easy to modify the above interface now

def task1(x: int, y: str, z: Optional<int>) -> int
   if z is None:
       z = 10

OR

def task1(x: int, y: str, z: int = 10) -> int

But, in the currently type system, Flyte type system, it is expected that the z value is bound from an upstream variable or a default is explicitly provided to the node.
A better approach would be that the platform automatically substitutes the default values or None for all optional variables, if not bound explicitly

Moreover,
python automatically converts the following into a Optional type

def foo(x: str = None)

and optional is only represented as a union

Union[str, NoneType

Thus now the users need to pass unions to all tasks, without automatically binding None

Goal: What should the final outcome look like, ideally?

remote tasks should automatically get None values if not specified

Describe alternatives you've considered

NA

Propose: Link/Inline OR Additional context

No response

Are you sure this issue hasn't been raised already?

• Yes

Have you read the Code of Conduct?

• Yes