Improve error message when multiple container image extensions are present

[geoand]

The error message now looks something like:

[ERROR] [error]: Build step io.quarkus.container.image.deployment.ContainerImageProcessor#publishImageInfo threw an exception: java.lang.IllegalStateException: quarkus-container-image-jib and quarkus-container-image-docker were detected, at most one container-image extension can be present.
[ERROR] Either remove the unneeded ones, or select one by setting any of the following configuration properties: 'quarkus.container-image.builder=docker','quarkus.container-image.builder=jib'

where it used to be:

[ERROR] [error]: Build step io.quarkus.container.image.deployment.ContainerImageProcessor#publishImageInfo threw an exception: java.lang.IllegalStateException: quarkus-container-image-jib and quarkus-container-image-docker were detected, at most one container-image extension can be present.
[ERROR] Either remove the unneeded ones, or select one by adding the property 'quarkus.container-image.builder=<extension name (without the container-image- prefix)>' in application.properties or as a system property.

Closes: #26589

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[iocanel]

LGTM