Merge extension catalog metadata properties when merging catalogs from different registries

[aloubyansky]

Description

The issue was discovered trying to setup an extension registry with a custom Quarkus platform.
The idea was to provide overrides for certain properties present in the Quarkus upstream platform catalogs for custom project creation.

Original discussion happened in https://quarkusio.zulipchat.com/#narrow/stream/187030-users/topic/custom.20create.20app.20scaffolding/near/469586566

FYI @vsevel

[maxandersen]

what are the "certain properties"?

[vsevel]

new properties to add, allowing to configure the way the pom should be generated (see also #42574):

• add a parent pom
• avoid generating properties
• avoid the dep mgmt section
• avoid the plugins except the quarkus maven plugin
• avoid adding a few dependencies that are fetched from our main extension: rest, config-yaml, ... => property

properties to change the FROM in dockerfiles (see also #42601):

• existing property dockerfile.native-micro.from
• new proposed property dockerfile.jvm.from