Accept a list of quarkus extensions in the quarkus-platform-bom-maven-plugin

[rsynek]

The quarkus-platform-bom-maven-plugin currently requires a BOM (e.g. org.optaplanner:optaplanner-bom) as an input to generate a platform member BOM (e.g. io.quarkus.platform:quarkus-optaplanner-bom).

The input BOM is supposed to define also versions of dependencies of all related Quarkus extensions, which forces the dependencyManagement of the project the extensions belong (e.g. https://github.com/kiegroup/optaplanner) to be split into two parts:
1/ dependencies of Quarkus extensions
2/ everything else
This approach creates a maintenance burden on the platform participant project and does not guarantee the dependencyManagement is correct; think of overriding the BOM in some other place in the participant project's structure.

The proposal is to pass the list of GAV of related Quarkus extensions and a single pom.xml file declaring dependencyManagement for the entire project. The quarkus-platform-bom-maven-plugin would then pick only those dependencyManagement entries from the pom.xml file that the extensions truly depend upon.

@aloubyansky I took the liberty of filing this issue so that we can track and further discuss what we talked about today.