Description
Is your feature request related to a problem? Please describe.
In PR #499, we need to serialize selector into a jsonable dictionary and then to initialize a new selector from that dictionary later, which requires us to store all the parameters from a selector. To instantiate a selector, we need to pass the input kwargs to the constructor, and the kwargs should be stored and serialized in some way that allows a new selector to be initialized by deserializing its intermediate representation (IR).
Describe the solution you'd like
As described in method 2 from #499 (comment), we may add a todict() and fromdict() to the base Selector class, where we can implement the serialization/deserialization of input kwargs and any necessary states of a selector. We also need to remove kwargs from the __init__ to avoid confusing behaviors of subclasses. Maybe it's better to put input kwargs into a default_configs() method and then propagate them in initialize() just like what PipelineComponent does so that todict() and fromdict() can be more straightforward.
The changes described above may deprecate a lot of interfaces related to Selector that was previously used, so maybe we should keep the implementation and method signatures (keep the __init__ signature) of the current selectors inherited from base class. But we need to override their todict()/fromdict() since the todict()/fromdict() in base Selector class may not apply to them.
Describe alternatives you've considered
Any suggestions/solutions for selector serialization/deserialization are welcome.
Additional context
Add any other context or screenshots about the feature request here.