ArC - register /quarkus/arc/beans and /quarkus/arc/observers routes in the dev mode

[mkouba]

• these routes produce basic debug info in the JSON format

How to use:

1. mvn quarkus:dev
2. HTTP GET http://localhost:8080/arc/beans
3. HTTP GET http://localhost:8080/arc/observers
4. simple filter Switch to the Maven distributed copy of the SubstrateVM annotations #1 - HTTP GET http://localhost:8080/arc/beans?scope=Singleton
5. simple filter Make it possible to use docker to build native images #2 -HTTP GET http://localhost:8080/arc/beans?beanClass=org.acme.Foo
6. simple filter First shot at integrating mp-metrics. #3 - HTTP GET http://localhost:8080/arc/beans?kind=PRODUCER_METHOD

This PR also contains a minimalistic JSON generator (io.quarkus.vertx.http.runtime.devmode.Json, mainly copied from the Weld Probe) because we can't use io.vertx.core.json.JsonObject/JsonArray unless the quarkus-jackson-databind extension is in.

[mkouba]

I should probably add some tests too.

[geoand]

This is a very userful feature, 👍

[cescoffier]

@mkouba Would it make sense to add a link on the generated "index.html" page to get this page?
Maybe also when an error is reported?

[mkouba]

@cescoffier it's not a page but a JSON file. It would probably make sense to provide an html page as well. That's the next step ;-).

[cescoffier]

Yes, definitely a next step. But can be cool to have a few ‘debug’ pages: beans, routes...

[geoand]

Yes, definitely a next step. But can be cool to have a few ‘debug’ pages: beans, routes...

Absolutely. This stuff then can also be used by IDEs (cc @maxandersen)

[mkouba]

#2120 is probably related...

[geoand]

It is yeah :)

[maxandersen]

these kind of debug pages - shouldn't we put them under one root, i.e. /devmode/ just to not "overcrowd" the name space ?

[mkouba]

There is an open issue for mgmt endpoints: #2450

+0 for the /devmode/ suffix...

Also it's not a debug page but a debug endpoint that returns a JSON file ;-).

[maxandersen]

you are +0 because of the suggested name or in principle ?

and yes #2450 is the same challenge for sure and it doesn't matter if its page or endpoint...its about having things "collected"