Update links to VCI IG

[p9g]

Several Links point to http://build.fhir.org/ig/dvci/vaccine-credential-ig/branches/main/ That link is to an older version of the IG. This IG was moved to HL7 github space.

Update the links to point to http://vci.org/ig/vaccination-and-testing

This link redirects to the current CI build of the IG in the HL7 space (currently https://build.fhir.org/ig/HL7/fhir-shc-vaccination-ig/ which should also remain stable; from that location, other versions can be found by following the "Directory of published versions" link at the top of every page).