[Feature Request]: Install package from CRAN instead of github releases

[averissimo]

Feature description

It seems odd that we use github as the source for packages on teal.gallery apps that users are encouraged to tweak.

• stable versions should use CRAN versions whenever possible.
  • Packages not released on CRAN may need a custom exception mechanism that indicates the github repository (could be a named list with package = "<github user>/<repository>")
• dev could use insights.engineering.r-universe.dev repository as part of the repos

This needs further refining and discussion with previous maintaner

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