Fix IWXXM 3.0 schematron rules for METAR/SPECI, AIRMET and SIGMET products.

[mgoberfield]

Fix IWXXM 3.0 schematron rules for METAR/SPECI, AIRMET and SIGMET products.

[blchoy]

Looking back these known bugs had been fixed in IWXXM 3.0-dev but this version has never been published after a debate. In order not to re-invent the wheel I have revived this branch and renamed it as v3.0.1RC1. I confirmed that both examples passed the schematron tests in iwxxm.sch. The remaining question is how to deal with this; are we going to leave it as a branch of the GitHub repository as unofficial materials? @amilan17 we need Secretariat's advise.

Note that even though I renamed the branch to v3.0.1RC1, the schema version is still indicated as 3.0-dev. If we decided to leave the branch there we will need to decide the version number the schemas should carry and make necessary adjustments.

[amilan17]

https://github.com/wmo-im/iwxxm/wiki/TT-AvData-Teleconference-2023-Jul-6 notes:

@mgoberfield will test branch.

@amilan17 will work on publication options for the MoC vI.2, schematron and notifications needed.
The ONLY change is the schematron.