MINOR: Extended Scala serdes implicit conversions with optional custom naming

[mowczare]

Since custom state store and repartition topic naming in DSL API is now possible in Kafka 2.1.0, this proposed feature enhance implicit conversions for the Scala API making it possible to call (assuming val stream: KGroupedStream[K, V]:

stream.aggregate(initializer)(aggregateFunc)("customNameTopic")

instead of:
stream.aggregate(initializer)(aggregateFunc)(Materialized.as[K, V, ByteArrayWindowStore]("customStateStoreName")

This change is backward compatible, that said: stream.aggregate(initializer)(aggregateFunc) also works with default naming convention.

These implicit conversions are propagated for Materialized, Grouped and Joined as well.

[mowczare]

summon @guozhangwang @debasishg @joan38 @bbejeck for review.

[joan38]

I like this still because it's the default in Scala but it seems that in this code base we adopted the Java style.
So for consistency I guess we should leave it to Java style or bigbang the whole codebase to Scala style.

You need to use gradle spotlessApply and commit the formatting change, then your Jenkins should pass.

[joan38]

These are redundant braces we don't need to add them.

gradle spotlessApply will solve it all for you.

[joan38]

This PR is going against the Scala spirit of type-safety.
This makes use of implicit conversion that the compiler team is trying hard to get rid of it (see scala/scala3#2060)

We should avoid as much as possible to use "primitive" types like Strings and use actual meaningful types:

stream.aggregate(initializer)(aggregateFunc)(Materialized.as("customStateStoreName"))

has a good compile time safety compare to:

stream.aggregate(initializer)(aggregateFunc)("customStateStoreName")

and even worst:

val materializerStore = "customStateStoreName"
stream.aggregate(initializer)(aggregateFunc)(materializerStore)

[joan38]

@mowczare hope this is not discouraging!
Thanks for the PR.
Also please don't hesitate to ask more questions on this! I'm always happy to provide more context.