Change default OPENHARMONY_VERSION to 3.0

As we are going to apply for OpenHarmony compatbibility certification using 3.0.1 baseline, we should change the default OpenHarmony version to this version.

This applies to the default OPENHARMONY_VERSION value, and as a consequence, the documentation related to OpenHarmony versions.

changed milestone to %goofy beta

set weight to 1

mentioned in merge request !39 (merged)

changed iteration to *iteration:13

assigned to @esben

mentioned in merge request !42 (merged)

mentioned in commit cfae56f5

closed with merge request !42 (merged)