Add the ability to set HTTP headers and Response status when returning Reactive Types from RESTEasy Reactive

[geoand]

Description

Currently when returning a Uni or Multi, there is no easy way to set a response header or a the HTTP status.
We should provide and document a way to do this.

Implementation ideas

There are two ways I can think of:

1. We introduce @Header and @Status annotations that can be placed on a resource method and if the method was executed properly, these annotations set the corresponding response properties.
2. We allow the use of RestResponse<Uni<T>> and RestResponse<Multi<T>>. This would allow more control, but might be more cumbersome to use.

WDYT @FroMage @stuartwdouglas ?

[quarkus-bot]

/cc @FroMage, @stuartwdouglas

[ambition-consulting]

Hate to be pushing again - but yes, we definitely need this. Not sure if we are the first enterprise application using reactive server+client with quarkus, but this stuff is fundamental!

[geoand]

We'll likely add this soon.

[FroMage]

Can't we return a Uni<RestResponse<>> ATM? The docs say we can from filters and exception mappers, so I assume we can from endpoints too.

[geoand]

I think that works, but it only covers that one use case. I'll open a POC PR for the annotations I proposed, soon

[geoand]

#20311 is what I had in mind

[mschorsch]

@geoand Is Flow<T> (Kotlin) also supported (#20345 )? I had this use case some days ago.

[geoand]

Yes it is. Feel free to comment about that on the Pull Request