Use the DOI provided by the CRAN

For a few days now, CRAN has been providing a DOI for each R-package. The airGR package now has 2 DOIs...
It may be better to use the CRAN DOI instead of the Datavserse one.

DOIs :

• CRAN: 10.32614/CRAN.package.airGRteaching
• entrepot.recherche.data.gouv.fr: 10.15454/W0SSKT

If so, change it in:

• the CITATION file
• the GitLab project badge
• the airGR website
• the HAL references for:
  • the manual
  • the software