Add the ability to generate equals and hashcode for @ConfigMapping

[ia3andy]

Currently, it's possible to generate toString as explained here:
https://smallrye.io/smallrye-config/Main/config/mappings/#tostring

But there is nothing for equals and hashcode.

The use case is for Quarkus extension config, without this, it's very ugly to deal with equals as shown in this PR:
quarkiverse/quarkus-quinoa#594

When this is done we should update the Quarkus writing extension guide to mention this.

[ia3andy]

cc @radcortez

[dmlloyd]

This relates to #1001 since those generated interfaces also need equals/hashCode, and should share as much code as possible.

[ia3andy]

@radcortez any update on this?

[radcortez]

Not yet... sorry @ia3andy. Let me try to prioritize this.