Extend companyCode in infrastructureManagers.xsd to alphanumeric

ERA's Organisation Code Register (OCR) extends the format of 4 digit UIC RICS codes by also allowing letters. We should therefore extend the pattern for companyCode in our Infrastructure Managers codelist.

The format is specified in Commission Implementing Decision (EU) 2018/1614 of 25 October 2018, Annex II, section 3.4.2.2

3.4.2.2. Format of organisation codes

For each of the four alphanumeric characters, any of the 26 letters of ISO 8859-1 alphabet or any number from 0 to 9 may be used. Letters are written in capitals.

The pattern should be changed from [0-9]{4} to [0-9A-Z]{4}.